There are many causes of thermal failure of lead-acid batteries. The failure mode is mainly divided into: dry failure mode, the failure mode of the capacity is premature loss, the failure mode of thermal out of control, the negative electrode is not reversed sulfate, the grid corrosion and elongation.First, dry failure mode
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Exhaust hydrogen, oxygen, water vapor, and acid fog is discharged from the valve-controlled lead-acid battery, which is the reason why the battery is watering and drying. This factor that drying causes battery failure is unique to the valve-controlled lead-acid battery. The cause of loss of water has four: 1 gas re-adherence is low; 2 from the battery housing; 3 grid corrosion consumption water; 4 self-discharge loss water.
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(1) Gas regeneration efficiency
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Gas regeneration efficiency and the selection of floating charge voltage are great. The voltage is selected too low, although there is less oxygen, high composite efficiency, but individual batteries will fail due to lack of long-term charging, so that the battery life is shortened. The floating charge voltage is too high, the amount of gas precipitation is increased, and the gas re-cooperation is low. Although the negative negative failure is avoided, the safety valve is frequently opened, and there is no water loss, the positive plate gate also has corrosion. Affect the battery life.
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(2) osmotective moisture from housing material
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The relevant performance of various battery housing materials is shown in the table below. As seen from the table, the water vapor permeability of the ABS material is large, but the strength is good. The permeability of the battery housing is related to its wall thickness, and the inner outer water vapor pressure difference in the housing is also in the housing material.
(3) Grid corrosion
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Grid corrosion also causes moisture consumption, and its reaction is:
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PB + 2H2O → PBO2 + 4H + + 4E-
(4) Self-discharge
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The oxygen from which the positive electrode from the precipitation may not be in the negative electrode, but the electrode precipitated hydrogen cannot be in the positive electrode, and the battery is accumulated, discharged from the safety valve, especially the battery is stored at a higher temperature. Self-discharge acceleration.
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Second, the failure mode of capacity premature loss
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The use of low bismuth or non-strait grid alloys in the valve-controlled lead-acid battery, early capacity loss often occurs in the following conditions:
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1 Not suitable circulatory conditions, such as continuous high speed discharge, deep discharge, and low current density at the start of charging;
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2 lack of special additives such as SB, SN, H3PO4;
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3 high-speed discharge utilization rate, the high level of electrolyte, and the electrolytic solution is too low;
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4 The active material is too low, the assembly pressure is too low.
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Third, the failure mode of thermal out of control
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Most battery systems have fever problems, which may be greater in the valve-controlled lead-acid battery, which is because the oxygen rescue process causes more heat in the battery; the amount of gas discharged is small, and the heat dissipation is reduced;
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If the valve-controlled lead-acid battery is too high, the charge device voltage is out of control, the battery charge will increase too fast, the internal temperature of the battery increases, the battery is dissipated, resulting in overheating, battery internal resistance, charging current Further, it is further increased, and the internal resistance is further reduced. This repeatedly formed a vicious circle until the thermal out of control causes the battery housing to be severely deformed, and it fits. In order to prevent the occurrence of heat loss, we must use corresponding measures:
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1 Charging equipment should have temperature compensation function or limit;
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2 Strictly control the quality of the safety valve to make the internal gas of the battery are discharged.
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3 The battery is set in a well ventilated position and controls the battery temperature.
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Fourth, negative electrode irreversible sulfate
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Under normal conditions, the lead storage battery forms the lead crystals of sulfate during discharge, which can be more easily reduced to lead during charging. If the battery is used and maintained, for example, it is often in low charge or over-discharge, and the negative electrode will gradually form a coarse hard sulfate, which is hardly dissolved, and it is difficult to charge it into an active substance with conventional methods. The battery capacity, even becomes the end of battery life, which is referred to as a polar non-reversible sulfate.
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In order to prevent irreperfarable sulfate inversion of negative electrodes, the battery must be charged in time, and unavailable.
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V. Grid corrosion and elongation
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In the lead-acid battery, the positive electrode plate grid is thicker than the negative electrode plate. When charging, in particular, when overcharge, the positive electrode plate gate is corroded, gradually being oxidized into a lead-free lead. Role, to compensate for its corrosion, we must thicken the positive plate gate.
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Therefore, in the actual operation, be sure to select a suitable floating voltage according to the ambient temperature, the floating voltage is too high, except that the water loss is accelerated, and the positive plate gate corrosion accelerates. When the alloy sheet is corroded, the stress is generated, causing the plate to deform, elongate, short-circuiting the polar edge or polar plate and the bus bar; and the life of the valve-controlled lead-acid battery depends on the polar plate life, its design life It is calculated according to the corrosion rate of the positive plate gate alloy, the more the positive pole grid is corroded, the less the remaining capacity of the battery; the shorter battery life.
The capacity of the lead-acid battery has a size, which determines the working time and life of the battery. The lead battery capacity is reduced with the discharge ratio. When it comes to the capacity, the time limit or magnification of the discharge must be specified. The battery capacity is different from the discharge rate or the magnification.
First, the impact of the discharge rate on battery capacity
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The lead battery capacity is reduced with the discharge ratio. When it comes to the capacity, the time or magnification of the discharge must be specified. The battery capacity is different from the discharge rate or the magnification.
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(1) Relationship between capacity and discharge rate
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For a given battery, discharge at different time rates, there will be different capacities, the following table is the rated capacity of the Huada GFM1000 battery at normal temperature at normal temperature.
(2) Reasons for the decline in capacity when high-magnification discharge
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The higher the discharge magnification, the larger the discharge current density, the more uneven distribution of the current on the electrode, and the current is preferentially distributed on the nearest surface of the main body electrolyte, thereby preferentially generate PBSO4 in the outermost surface of the electrode. The volume of PBSO4 is larger than PbO2 and Pb, so that the discharge product is blocked by the porous electrode, the electrolyte does not sufficiently supply the internal reaction of the electrode, and the internal material in the electrode cannot be fully utilized, so that the capacity of high magnification is lowered.
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(3) Depth relationship between discharge current and electrode
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At a high current discharge, the active material is limited in the thickness direction, the smaller the current, the smaller the degree of active substance is utilized, the smaller the capacity given by the battery. When the electrode is discharged at a low current density, when i ≤ 100A / m2, the active material has a depth of 3 × 10-3 m-5 × 10-3m, and the inner surface of the porous electrode can be taken completely. When the electrode discharges at a high current density, when I ≥ 200A / m2, the active material has a sharp drop, about 0.12 × 10-3m, and less use in the depth of the active substance, when the diffusion has become a decision of restriction capacity factor.
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At the current discharge, due to the presence of polarization and internal resistance, the end voltage of the battery is low, and the voltage drop loss is increased, so that the battery end voltage is low, and the capacity is also affected.
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Second, the effect of temperature on battery capacity
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The ambient temperature has a large amount of capacity of the battery, and the capacity is reduced as the ambient temperature is lowered. The battery capacity change at 1 ° C in ambient temperature is called the temperature coefficient of the capacity.
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According to national standards, if the ambient temperature is not 25 ° C, the measured capacity is required to convert the actual capacity Ce at 25 ° C based in the following formula, and its value should meet the standard.
CE = CT / [1 + K (T-25 ° C)]
In the formula: T is ambient temperature at the time of discharge
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K is a temperature coefficient, and the capacity of 10HR is k = 0.006 / ° C, and the capacity of 3HR of 3HR is k = 0.008 / ° C, and the capacity of 1HR is k = 0.01 / ° C.
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Third, the calculation of the capacity of the valve controlled battery
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The actual capacity of the valve-controlled lead-acid battery is related to the discharge system (discharge ratio, temperature, termination voltage) and the structure of the battery. If the battery is discharged at a constant current, discharged to a predetermined termination voltage, the actual capacity CT = discharge current I × discharge time t, the unit is AH. Recommend: LiFePO4 Battery Manufacturer Energy storage battery Manufacturer Integrated machine energy storage battery series Manufacturer Lead lithium battery Manufacturer Outdoor Backup Battery Manufacturer Portable outdoor power supply Manufacturer Power battery Manufacturer Powerwall LiFePO4 Battery Manufacturer Battery rack Manufacturers Telecom LiFePO4 Battery Manufacturer Wall mounted battery storage Manufacturer China Lifepo4 Battery
