The role of AGM Separator in batteries:
1. Prevent short circuit between positive and negative plates in the battery
2. Fix electrolyte
3. Provide hydrogen-oxygen recombination channels during charge and discharge to prevent active material shedding from both electrodes.
4. Slowdown the formation of lead dendrites and reduce electrolyte loss during charge and discharge.
5.Make the battery maintenance-free or reduce maintenance to extend service life
The excellent properties of AGM separators include:
Excellent corrosion resistance; fast absorption of electrolyte; uniform thickness; good insulation properties; and a long service life, in addition to their porosity.
Overview
An AGM separator is a thin, nonwoven mat of micro‑fibrous glass that immobilizes the sulfuric acid electrolyte in a valve‑regulated lead–acid (VRLA) cell, enables ion transport, and provides electrical insulation between positive and negative plates. Typical glass fibers are 0.25–4 μm in diameter with a mean length near 1 mm, yielding a highly porous, acid‑wettable structure with very low internal resistance and excellent mechanical robustness—key to high‑rate discharge and reliable cycling performance.
Core functions
Electrolyte immobilization and uniform distribution
The separator holds the electrolyte to create a “recombinant” cell where gas‑phase transport is confined and controlled. It must keep the acid uniformly distributed to suppress acid stratification and electrolyte drainage, both of which accelerate degradation. In VRLA designs, the AGM is the primary acid reservoir between plates.Oxygen recombination pathway and water conservation
During overcharge, oxygen generated at the positive plate migrates through the partially saturated separator pores to the negative plate and is reduced to water. The separator’s pore structure must balance gas permeability with acid inventory so that recombination proceeds efficiently while allowing the negative plate to recharge before excessive oxygen reduction occurs—minimizing water loss and maintenance.Electrical insulation and ionic conduction
AGM provides dielectric isolation between plates to prevent internal short circuits while its high porosity and wettability maintain low ionic resistance for good high‑rate discharge and charge acceptance.Mechanical support and pressure maintenance (wet‑elasticity)
The mat must retain plate‑group pressure when wet to maintain intimate plate–separator contact and consistent ionic pathways. This “wet‑elasticity” suppresses positive active‑material expansion and premature capacity loss (PCL2) during cycling.Dendrite mitigation and structural integrity
Sufficient tensile strength, modulus, elongation, and puncture resistance reduce the risk of short circuits from dendrite growth and manufacturing defects, ensuring stable performance over life.
Design parameters and trade‑offs
| Parameter | Why it matters | Typical target or behavior |
|---|---|---|
| Fiber diameter and specific surface area | Controls wettability, capillary hold-up, and mechanical strength; finer fibers increase surface area and acid retention but can raise resistance if not optimized. | Fibers commonly 0.25–4 μm; high specific surface area improves uptake and wetting. |
| Porosity and pore structure (tortuosity, interconnectivity) | Determines acid inventory, ionic path length, and gas permeability; must enable recombination without excessive acid drainage. | Typical AGM porosity >90%; typical saturation in operation around 93–96% to reserve gas channels. |
| Thickness and compression behavior | Affects pressure on plates (wet‑elasticity), acid distribution, and internal resistance; too soft loses contact, too stiff impedes conformability. | Designed for target thickness and compression set to maintain contact across rates and cycles. |
| Wettability and acid uptake | Ensures uniform filling, fast wet‑out, and stable distribution; prevents dry spots and stratification. | High acid uptake and uniform wettability are essential; structure tailored to application rates and DoD. |
| Mechanical strength and puncture resistance | Prevents short circuits from manufacturing defects or dendrite growth under pressure cycling. | High tensile modulus/strength and elongation; robust to handling and assembly. |
| Gas permeability and saturation setpoint | Must allow sufficient O₂ flux for recombination while avoiding over‑saturation (flooded behavior) or under‑saturation (high diffusion losses). | Typical operating saturation 93–96%; pore network provides defined gas pathways. |
Typical applications and performance implications
UPS and telecom standby
Prioritize long float life, voltage stability, and minimal water loss; AGM’s low resistance and efficient recombination suit high reliability, low‑maintenance service.Automotive start‑stop and motive power
Require high‑rate discharge and vibration resistance; AGM’s low internal resistance and robust mechanical properties support cranking and dynamic loads.Deep‑cycling applications
More challenging for AGM due to positive plate expansion and stratification risks; separator design (wet‑elasticity, pore structure, acid distribution) must be optimized for the intended depth‑of‑discharge (DoD) and cycle profile.
