Factors affecting the life of lead acid batteries

The failure of lead acid battery is the result of many factors, which is determined by the internal factors of the plate, such as the composition of active substances. Crystal form, porosity, plate size, grid material and structure also depend on a series of external factors, such as discharge current density, electrolyte concentration and temperature, discharge depth, maintenance status and storage time. Here are the main external factors.

2.1 Depth of discharge

The depth of discharge is the degree to which the discharge starts and stops during use. 100% depth means full capacity release. The life of lead-acid batteries is greatly affected by the depth of discharge. The key point of design consideration is deep cycle use, shallow cycle use or floating charge use. If a shallow cycle battery is used for a deep cycle, the lead-acid battery will quickly fail.

Because the positive active material lead dioxide itself is not firmly bonded to each other, lead sulfate is generated during discharge, and it returns to lead dioxide during charging. The molar volume of lead sulfate is larger than that of lead oxide, so the volume of the active material expands during discharge. If one mole of lead oxide is converted to one mole of lead sulfate, the volume increases by 95%. In this way, the repeated shrinkage and expansion will gradually loosen the mutual bonding between the lead dioxide particles, which is easy to fall off. If only 20% of the active material of one mole of lead dioxide is discharged, the degree of shrinkage and expansion will be greatly reduced, and the damage of the binding force will be slow. Therefore, the deeper the discharge depth, the shorter the cycle life.

2.2 Degree of overcharge

A large amount of gas is precipitated during overcharging. At this time, the active material of the positive plate is subjected to the impact of the gas, which will promote the falling off of the active material; In addition, the positive grid alloy also severe anodization and corrosion, so the battery life will be shortened when the battery is overcharged.

2.3 The influence of temperature

Lead-acid battery life increases with temperature. Between 10°C and 35°C, for every 1°C increase, approximately 5 to 6 cycles are added, and between 35°C and 45°C, each increase of 1°C can prolong the life for more than 25 cycles; Above 50℃, the life is reduced due to the loss of vulcanization capacity on the negative electrode.

Battery life increases with temperature over a range,because capacity increases with temperature. If the discharge capacity remains unchanged, the depth of discharge decreases when the temperature increases, and the life is extended.

2.4 Effect of sulfuric acid concentration

The increase of acid density is beneficial to the capacity of the positive plate, but the self-discharge of the battery increases, the corrosion of the grid also accelerates, and it also promotes the looseness and shedding of lead dioxide. With the increase of acid density in the battery, the cycle life decreases.

2.5 Effect of discharge current density

As the discharge current density increased, the life time of the battery decreased because under the condition of large current density and high acid concentration, the positive lead dioxide was prompted to fall off loosely.

Another failure mode is loss of water. For open batteries, water loss is a normal maintenance, and for sealed batteries, it should not occur under strict control. Therefore, water loss is not included in the failure mode. The problem of water loss from sealed batteries is mostly electric bicycles. It is because the constant voltage value of charging is too high.