Failure Reasons of Lead-Acid Batteries and Their Repair Methods

Since French scientist Gaston Planté invented the lead-acid battery in 1859, it has been widely used in transportation, communications, power, railways, mining, ports, defense, computers, and scientific research due to its high safety, low cost, and excellent recyclability. It remains the most produced and versatile battery type globally.

Lead-acid batteries offer several advantages in applications: low price, mature technology, excellent high- and low-temperature performance, stability, reliability, high safety, and good resource recyclability, giving them a clear market edge. By 2020, China's lead-acid battery market reached 165.9 billion yuan, growing 4.65% year-over-year.

As market share grows, issues like massive energy consumption during production and recycling, plus billions of discarded batteries annually causing severe environmental pollution, have intensified. Maintaining and repairing aged batteries to boost efficiency and lifespan has become a global priority.

In developed Western countries, tens of thousands work in lead-acid battery maintenance, repair, and recycling, generating billions in annual revenue. Japan employs over 100,000 in the sector, also yielding billions.

In China, to promote energy conservation and environmental protection, a 4% consumption tax on lead-acid batteries was imposed starting January 1, 2016. The "Technical Policy on Waste Battery Pollution Prevention" by the State Environmental Protection Administration, NDRC, Ministry of Construction, MOST, and MOFCOM encourages R&D for efficient recycling, raising resource recovery rates.

Experts note that performance degradation and premature failure mainly stem from lead sulfate crystals forming on plates during use, increasing internal resistance and reducing capacity, ultimately shortening life. Proven techniques for repairing lead-acid batteries extend lifespan, cut costs, reduce waste like lead and dilute sulfuric acid, lower CO2 emissions, and conserve resources—aligning with sustainable development.

In an era of rising energy use and battery pollution, solving waste reuse, extending life via repair tech, curbing discards, and promoting sustainable paths hold profound significance. Repair tech turns waste into treasure, fits national policies, boosts economy while advancing "energy-saving and emission-reduction," and aids environmental protection, poised for wider adoption.

To grasp lead-acid battery repair, first understand failure reasons, then address repair methods accordingly.

Failure Reasons of Lead-Acid Batteries

Due to variations in plate types, manufacturing, and usage, failure causes differ. Common reasons include:

1. Corrosion and Deformation of Positive Plates

Current alloys fall into three categories: traditional lead-antimony (4-7% antimony); low/ultra-low antimony (<2% or <1%, with tin, copper, cadmium, sulfur); and lead-calcium (0.06-0.1% calcium, with tin and aluminum). During charging, these grid alloys oxidize to lead sulfate and PbO2, losing support for active materials and causing failure. PbO2 corrosion layers induce stress, enlarging grids; deformation over 4% destroys plates, loosens active materials, or shorts at busbars.

2. Shedding and Softening of Positive Plate Active Materials

Beyond grid expansion, repeated charge-discharge cycles loosen PbO2 particle bonds, causing softening and shedding. Grid manufacturing, assembly tightness, and charge-discharge conditions influence this.

3. Irreversible Sulfation

Over-discharge and prolonged storage in discharged state form coarse, hard-to-charge lead sulfate crystals on negative plates. Mild cases recover with methods; severe ones render electrodes inert.

4. Premature Capacity Loss

With low-antimony or lead-calcium grids, capacity drops sharply after ~20 cycles, causing early failure.

5. Severe Antimony Accumulation on Active Materials

Antimony migrates from positive grids to negative active surfaces during cycles. Lower H+ reduction overpotential (~200 mV) on antimony boosts water decomposition, preventing normal charging and leading to failure. Tests show 0.12-0.19% antimony on failed negative surfaces at 2.30V charge voltage. In submarine batteries, excess hydrogen links to 0.4% average antimony.

6. Thermal Failure

For low-maintenance batteries, charge voltage should not exceed 2.4V/cell. Faulty regulators can spike voltage, overheating electrolyte, dropping resistance, and amplifying current in a runaway cycle, deforming or cracking the battery. Though uncommon, monitor high voltage and heat.

7. Corrosion of Negative Busbars

Negative grids and busbars rarely corrode, but in sealed valve-regulated batteries, oxygen cycles fill headspace; electrolyte creeps to busbars via tabs, oxidizing alloys to lead sulfate. Poor welds accelerate this, detaching tabs and failing negatives.

8. Short Circuits from Separator Puncture

Some separators like PP have large pores; displaced melt-through fuses create big holes, allowing active materials to pass during cycles, causing micro-shorts and failure.

Factors Affecting Lead-Acid Battery Lifespan

Failure results from intrinsic factors (active material composition, crystal type, porosity, plate size, grid material/structure) and extrinsic ones (discharge density, electrolyte concentration/temperature, depth of discharge, maintenance, storage). Key externals:

1. Depth of Discharge

This is how far discharge proceeds before stopping (100% = full capacity). Lifespan varies greatly; deep-cycle batteries suit shallow use, but shallow ones fail quickly in deep cycles. PbO2 bonds weaken from volume changes: PbO2 to PbSO4 expands 95% molar volume. Shallow discharge (e.g., 20%) minimizes expansion/contraction, slowing degradation; deeper discharge shortens cycles.

2. Extent of Overcharge

Excess gas evolution impacts positive active materials, promoting shedding; grid alloys corrode via anodic oxidation, shortening life.

3. Temperature Effects

Lifespan generally rises with temperature up to 50°C: +5-6 cycles per 1°C from 10-35°C; +25+ cycles per 1°C from 35-45°C. Above 50°C, negative sulfation cuts capacity. Higher temperatures boost capacity, reducing effective depth for fixed discharge, extending life.

4. Sulfuric Acid Concentration Effects

Higher density aids positive capacity but increases self-discharge, grid corrosion, and PbO2 loosening/shedding, shortening cycles.

5. Discharge Current Density Effects

Higher density shortens life by accelerating PbO2 loosening under high current/acid conditions.

Water loss isn't a failure reason for vented batteries (normal maintenance) or sealed ones (avoidable). In sealed e-bike batteries, it arises from excessive constant voltage charging.

Repair Methods for Premature Capacity Loss (PCL)

(A) Characteristics of PCL

In low-antimony or lead-calcium grid batteries, capacity drops ~5% per cycle after ~20 cycles, failing early. Lead-calcium types often show unexplained drops in a few cells; positives aren't softened but capacity is low.

(B) Solutions for Causes

1. Optimize positive plate tin content (1.5-2% for deep-cycle).
2. Increase assembly pressure.
3. Avoid high electrolyte acid content.

(C) Usage Precautions

1. Avoid sustained low initial charge currents.
2. Minimize deep discharges.
3. Limit overcharge.
4. Don't boost capacity via high active material utilization.

(D) Recovery for PCL-Affected Batteries

Start with 0.3C-0.5C current, then trickle charge to full. Store charged batteries at 40-60°C; discharge at <0.05C to 0V (slow after half nominal voltage). Repeat to restore capacity.

(E) Notes

Confirm PCL in first 20 cycles; later drops worsen with this method, softening positives. In lead-calcium batteries, imbalance from low-voltage constant chargers causes issues: unequal self-discharge leads to chronic undercharge in some cells (sulfation) and overcharge in others. Use multi-stage chargers with varying current/voltage, ending in high-voltage low-current balance charge.

Overcharge Repair

Overcharge demands high current/voltage, causing side reactions, positive damage, and water loss. An effective non-damaging method is pulse charging: high-voltage/current pulses overcome acceptance decline without sustained reactions, leveraging battery depolarization (or aids) post-pulse. This enables safe overcharge, with chargers proven over years to greatly extend cycle life.