Monitoring technology and application of battery internal internal resistance in DC power supply system - News - Global IC Trade Starts Here 工业

MOS Power IC Full Range

Probe Current Voltage Pin 420x4450 Head Diameter 5.0 Overcurrent Current and Voltage Pin

Brand AVX TPSE226M035R0125 Low Impedance Tantalum Capacitor AVX 22

Inductance

1 Overview

Currently, valve-regulated lead-acid batteries are widely used in electric power supply and communication power systems. Due to the unique structure of these batteries, it has become challenging yet crucial to monitor their performance effectively during operation and perform targeted maintenance. Various battery monitoring systems have been deployed extensively in power systems due to their high reliability requirements. Different testing methods provide insights into various aspects of the battery's performance. Years of research and practical applications have demonstrated that internal resistance testing is one of the most reliable methods. The different failure modes of the battery are reflected differently in its internal resistance. Understanding the relationship between the battery's internal resistance and various failure modes, and analyzing the internal resistance data of valve-regulated lead-acid batteries appropriately, can significantly aid in testing and maintaining the battery. Recently, with the rising costs of raw materials, many domestic manufacturers of valve-regulated lead-acid batteries have adopted innovative production techniques. These advancements have necessitated a reevaluation of how we analyze internal resistance data for these new-process batteries. Selecting appropriate benchmarks for such battery internal resistance data can greatly assist in assessing the performance of valve-regulated lead-acid batteries. Utilizing internal resistance data wisely can extend the battery's lifespan and yield significant safety and economic benefits.

2 Common Battery Failure Modes

For valve-regulated lead-acid batteries, typical performance degradation mechanisms include water loss, plate group corrosion, shedding of active materials, passivation due to deep discharge, and recovery after deep discharge. Below are descriptions of several cases of performance degradation:

(1) Battery Water Loss

Water loss in lead-acid batteries causes the electrolyte's specific gravity to increase, leading to corrosion of the positive grid and a reduction in the battery's active material, thus decreasing its capacity and causing failure.

In the later stages of valve-regulated lead-acid battery charging, the oxygen released from the positive electrode reacts with the negative electrode, forming water:

O₂ + 2Pb → 2PbO

PbO + H₂SO₄ → H₂O + PbSO₄

The negative electrode remains undercharged due to the oxygen, preventing the generation of hydrogen gas. This oxygen is absorbed by the lead of the negative electrode, continuing the water synthesis process, known as cathode absorption.

In the cathode absorption process, the generated water cannot escape under sealed conditions, allowing the valve-regulated sealed lead-acid battery to avoid supplementary water maintenance. This is why these batteries are sometimes referred to as "maintenance-free." However, during charging, when the voltage exceeds 2.35 V/cell, gas may escape. At this point, the battery generates a large amount of gas in a short period, which cannot be absorbed by the negative electrode. When the pressure exceeds a certain level, the one-way exhaust valve begins to vent, filtering out acid mist through the acid pad. Nevertheless, the loss of gas within the battery still equates to a loss of water. Thus, valve-regulated sealed lead-acid batteries require strict charging voltage control and must never be overcharged.

(2) Sulfation of Negative Plates

The primary active material of the negative grid is sponge-like lead. During charging, the following reaction occurs in the negative grid:

PbSO₄ + 2e⁻ → Pb + SO₄²⁻

An oxidation reaction occurs on the positive electrode:

PbSO₄ + 2H₂O → PbO₂ + 4H⁺ + SO₄²⁻ + 2e⁻

The chemical reaction during the discharge process is the reverse of this reaction. When the charge of a valve-regulated sealed lead-acid battery is insufficient, PbSOâ‚„ accumulates on both the positive and negative grids. PbSOâ‚„ loses its activity for an extended period, ceasing to participate in chemical reactions, a phenomenon known as active material sulfation. To prevent sulfation, the battery must always remain fully charged, and over-discharge must be avoided.

(3) Positive Plate Corrosion

Due to water loss in the battery, the electrolyte's specific gravity increases, and the excessively strong acidity accelerates the corrosion of the positive electrode plate. Preventing electrode plate corrosion is essential to avoid the battery's water loss phenomenon.

(4) Thermal Runaway

Thermal runaway refers to the cumulative enhancement of charging current and battery temperature during constant voltage charging, which progressively damages the battery. The root cause of thermal runaway is excessive float voltage.

Typically, the float charge should be set to (2.23 ~ 2.25) V/monomer (at 25°C), which is more appropriate. If this range is not followed, for instance, using 2.35 V/monomer (at 25°C), thermal runaway may occur after 4 months of continuous charging; or using 2.30 V/monomer (at 25°C), thermal runaway may occur after (6~8) months of continuous charging; if 2.28 V/monomer (at 25°C) is used, severe capacity decline may occur within (12~18) months, leading to thermal runaway. The direct consequence of thermal runaway is a bulging and leaking battery case, reduced capacity, and eventual failure.

3 Research on Internal Resistance Model of Valve-Regulated Lead-Acid Battery

Impedance analysis is a common method in electrochemical research and a necessary tool for battery performance studies and product design [10].

Figure 3-1 shows the equivalent circuit of the common lead-acid battery impedance.

[3]