Due to differences in the types of electrode plates, manufacturing conditions, and use methods, the causes of battery failure ultimately vary. To sum up, the failure of lead-acid batteries has the following situations:
1.Corrosion modification of positive plate
There are three types of alloys currently used in production: traditional lead-antimony alloys with antimony content of 4% to 7% mass fraction; low- or ultra-low antimony alloys with antimony content of 2% mass fraction or less than 1% mass Fraction, containing tin, copper, cadmium, sulfur and other modified crystal agents; lead-calcium series, is actually a lead-calcium-tin-aluminum quaternary alloy, the content of calcium is 0.06% to 0.1% mass fraction. The positive electrode grid made of the above alloys will be oxidized to lead sulfate and lead dioxide during the charging process of the battery, which will eventually lead to the loss of the supporting active material and cause the battery to fail. The alloy generates stress and deforms the grid. When the deformation exceeds 4%, the entire electrode plate will be destroyed, the active material will fall off due to poor contact with the grid, or it will be short-circuited at the bus bar.
2.The active material of the positive plate falls off and softens
In addition to the growth of the grid that causes the active material to fall off, as the charge and discharge are repeated, the bond between the lead dioxide particles will relax, soften, and fall off the grid. A series of factors such as the manufacture of the grid, the tightness of the assembly, and the charge and discharge conditions all have an effect on the softening and shedding of the positive plate active material.
3.Irreversible sulfation
When a battery is over-discharged and stored in a discharged state for a long time, its anode will form a kind of coarse lead sulfate crystals that are difficult to accept charging. This phenomenon is called irreversible sulfation. Slight irreversible sulfation can be restored by some methods. In severe cases, the electrode fails and cannot be charged.
4.Premature loss of capacity
When low antimony or lead-calcium is a grid alloy, a sudden decrease in capacity occurs during the initial period of use of the battery (about 20 cycles), causing the battery to fail.
5.Serious accumulation of antimony on active substances
The antimony on the positive electrode grid is partially transferred to the surface of the negative electrode active material with the cycle. Because the reduction of H + on antimony is about 200mV lower than that on lead, the charging voltage decreases when antimony accumulates. Part of the current is used for water decomposition, and the battery cannot be charged normally and thus fails.
After testing the antimony content of the negative electrode active material of the lead-acid battery that failed with a charging voltage of only 2.30V, it was found that the antimony content in the surface layer of the negative electrode active material reached 0.12% to 0.19% by mass. For some batteries, such as submarine batteries, there are certain restrictions on the hydrogen evolution of the battery. Tests have been performed on the negative electrode active material of hydrogen storage cells, and the average antimony content has reached 0.4% by mass.
6. Thermal failure
For less maintenance batteries, it is required that the charging voltage does not exceed 2.4V per cell. In actual use, for example, in a car, the voltage regulating device may run out of control, the charging voltage is too high, so the charging current is too large, and the heat generated will increase the temperature of the battery electrolyte and cause the internal resistance of the battery to decrease. Enhanced charging current. The temperature rise and excessive current of the battery reinforce each other, and ultimately cannot be controlled, causing the battery to deform, crack and fail. Although thermal runaway is not a frequent failure mode for lead-acid batteries, it is not uncommon. Pay attention to the phenomenon of excessive charging voltage and battery heating during use.
7.Corrosion of negative bus
In general, there is no corrosion problem on the negative electrode grid and the busbar, but in the valve-regulated sealed battery, when the oxygen cycle is established, the upper space of the battery is basically full of oxygen, and the busbar is more or less the electrolyte along the electrode in the diaphragm. Crawl up to the bus. The alloy of the bus bar will be oxidized to further form lead sulfate. If the alloy of the bus bar electrode is not selected properly, there will be slag inclusions and gaps in the bus bar. Corrosion will deepen along these gaps, resulting in the disconnection of the tabs from the bus bar and the failure of the negative plate.
8. Short circuit caused by diaphragm perforation
Some kinds of diaphragms, such as PP (polypropylene) diaphragms, have large pore diameters, and the PP fuse will shift during use, resulting in large pores. The active material can pass through the large pores during charging and discharging, causing micro short circuits. To make the battery ineffective.
