1. The AGM Wet performance and its application to the VRLA battery
Sinoma Science & Technology Co., LTD. Shuangwei Division
Yaozong Bai, Weihai Shen, Haijie Wang, Xupeng Dai

2. Abstract
With the development of VRLA Battery technology， The knowledge about application and the influence of the separator to the battery has been acquired more and more. In this work, we research the wet performance of the AGM separator and its action to the VRLA battery. For the different kinds of VRLA battery or for the different battery with the different application, AGM plays the different roles, whereas there are definitely some general characteristics. From this report we will disclose the relationship between recipes of the AGM raw materials, the compression sustain capability, the acid absorption under the pressure, the wet resilience and the frequency of the resilience to that of behaviors of the battery. So the suitable fine fiber and coarse fiber ratio and some recommended wet performance of the separators are introduced.

3. 1、Introduction
___ AGM separators are very important parts of VRLA battery and be considered as the “the third plate” of the battery.
___ Most of VRLA battery manufacturers paid much of their attention to the dry state performance of AGM like thickness, basic weight, tensile strength and acid absorption before.
___Now it has reached a consensus that the wet state performances of AGM such as resilience capability in wet state when the AGM is compressed, acid absorption under pressure are much more important.
___Sinoma Science & Technology Co., LTD. Shuangwei Division is the first AGM manufacturer in China and did much work in researching wet performances of the AGM separator. Now some of wet performances of AGM have been listed into our standard. See Table 1.

4. Table 1. AGM’s special function for different battery
1、Introduction
Table 1. AGM’s special function for different battery
Types of battery
The special function of AGM separator
keep the pressure inside the battery and extend the cycle life
Big Battery
Keep the shape of the separator
Keep consistency of the assembling thickness
Keep close contact of plate and separator
Holding the acid absorption after the battery be assembled
Middle Battery
extend the cycle life
Holding the acid absorption after the battery be assembled
Small Battery
Increase the porosity and the oxygen recombination efficiency

5. 2、Experiment 2.1．Raw Materials
Fine fiber（F）—the diameter of the fiber <1.5μm，
Coarse fiber(C)—the diameter of the fiber >1.5μm。
2.2.　Experiment process
The above fiber be chosen and mixed in different recipe and be made into AGM separators which with the same thickness. These 3 recipe are listed below. This paper will discuss these 3 AGM’s wet performances.
SW-1
SW-2
SW-3
Fine fiber
（F）% 90 70 40
Coarse fiber　(C)% 10 30 60

6. 3、 Result and Discussion
3.1 Test result
3.1.1 SEM photos of 3 kinds of AGM 　
Fig 1. SEM photos of sw-1, sw-2, sw-3

7. 3、 Result and Discussion
3.1.2 Test result of Basic weight and the porosity　
SW-1
SW-2
SW-3
Basic weight g/m2.mm（10kpa）
150
140
133
Porosity（%）
93.88
94.29
94.57

8. Two definition about wet performances
1、 pressure sustain capability at wet state
2、The wet resiliency of the AGM
The wet resiliency of the AGM means the wet AGM’s pressure variation that acting on the plate, after the battery be assembled; the acid be added and the whole cell be compressed.
The wet resiliency includes resilience capability and the resilience times. This value obtained by testing wet AGM’s thickness recovering capability after it is pressed. It can evaluate whether the AGM can keep the internal pressure of the battery during the whole cycle life.
It’s means the AGM ‘s capability to keep the pressure at some fixed acid saturation degree. It’s tested with the device shown in the photos. First the AGM was pressed to 50Kpa, then the acid was filling gradually. There is a pressure sensor be connected and can record the variation of the pressure. The pressure value when the acid absorption in saturation state is recorded. This value is pressure sustain capability.
Fig 2. pressure sustain capability test instrument

9. 3、Result and Discussion
3.2 pressure sustain capability at wet state
Fig AGM’s pressure sustain capability curve

10. 3、Result and Discussion
From above graph we know that the recipe of the fiberglass play important role in pressure sustain capability or the wet resiliency of the AGM.
The AGM contain more coarse fiber provides good wet resiliency or the pressure sustain capability. It’s final pressure inside the battery when the acid in saturation state is higher than fine fiber AGM. So if we want to keep high pressure between AGM and plate, or want to get the AGM with high resiliency, some more percentage of coarse fiber should be added
With the increasing of the saturation of the electrolyte the AGM separator which with high basic weight can supply high pressure reducing speed to the plate. The batteries’ final pressure which use high basic weight separator is 5% less than that use low basic weight AGM. This will also affect whole cell’s pressure.

11. 3、Result and Discussion
3.3 acid absorption at the pressure (simply write “acid absorption”)
Fig 4. acid absorption curve

12. 3、Result and Discussion
Form the above graph we know that for AGM with different basic weight, with the battery assembling pressure increasing the acid absorption of AGM decreasing. At different assembling pressure the low basic weight AGM corresponds to higher acid absorption.
The acid absorption depends on the internal pore structure of AGM , that means the porosity can affect the acid absorbing quantity. So for the VRLA battery, the high porosity is very important.
The reason of the importance of the porosity is:
----without enough porosity no enough acid can be added and it will affect the discharge capacity of the battery or let this value be reduced.
----If the electrolyte quantity be limited, the active materials of the plate can not be used entirely.

13. 3、Result and Discussion
3.4 wet state resiliency
Fig The AGM’s wet Thickness at different Pressure

14. Fig. 5 shows the thickness curve( at 10 Kpa) after the wet AGM be pressed under different pressure. It tested by pressing wet AGM in Kpa pressure for 30s’ and then test the 10Kpa thickness at the pressed pointed again. The 3 blue curves shows 10Kpa thickness change ration, or the thickness recovering ability after being pressed. It can evaluate whether AGM with good pressure keeping ability during the battery cycle life.
From this curve we know that AGM contains more fine fiber has good press resistant or good resiliency. And the AGM contains more coarse fiber also has good press resistant or good resiliency. When there is a suitable proportion of coarse fiber to fine fiber, some more loose structure may form and it can supply high compression.
The colors curve shows the wet AGM’s thickness at these pressures.

15. 3、Result and Discussion
3.5 compression-resiliency alternate test
Fig 6. Wet AGM compression-resiliency alternate test 　

16. This curve shows the wet AGM’s thickness recovering ability being pressed at the 10Kpa and 50Kpa pressure alternately. Here the 10Kpa and 50Kpa wet thickness was test alternately, the alternate time is 30s. The 10Kpa and 50Kap thickness was recorded and be made into this curve.

17. From Fig. 6 we know that different AGM have different wet resiliency
From Fig. 6 we know that different AGM have different wet resiliency. Coarse fiber AGM with better wet resiliency comparing to that of fine fiber AGM. Even in the initial press action period the coarse fiber AGM has some big compression. After experienced many times of press, the coarse fiber AGM keep high thickness reservation or keep high internal pressure.
For the wet AGM it’s pressure become smaller and this was caused by following 2 reasons :
The loosen of fiber-fiber’s combination. This is an irreversible process which made some tighter structure among the fibers.
2) When the AGM in wet state the pressure inside pore is reduced, This reduced pressure can transfer to the contacting plate.

18. 3、Result and Discussion
3.6 stratification
Fig 7. Stratification of different series AGM

19. Stratification means the density changing of the electrolyte in the height direction of the battery. Low density corresponds with high position.
We add the acid from the top of the AGM, which is hanged between two pressed board. The initial pressure is 50Kpa. After 24 hours, the acid density in each AGM’s height position is tested. Fig. 7 shows the results of different series AGM.
Its found that high basic weigh AGM (or AGM contain more fine fiber) has good ability to resistant the stratification, and can extend the cycle life of the battery.

20. thickness controlling at different pressure
4、Conclusion
From all the above discussion we know that the AGM with different fiber recipe can supply different performance and can meet different battery’s demands. According to these research Sinoma developed different AGM series can meeting different VRLA batteries’ application. See Table 4.
Table 4. AGM specification meeting different batteries’ demands
Type of Battery
Type of AGM
Specification of AGM
Big Battery
SW-1
Wet resiliency
Acid boiling
thickness controlling at different pressure
Pressure sustain capability
Acid absorption at pressure
Middle Battery
SW-2
Small Battery
SW-3
Basic weight

21. Thank You!