TBLS+ - Tetra Basic Lead Sulphate TBLS paper LABAT Ed1_July 2008.pdf · PENOX GmbH 1st Edition...

PENOX GmbH 1st Edition TBLS+® Technology

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by David Hardy & Ian Klein, PENOX GmbH

The formation of a homogenous tetra-basic sulphate crystal structure in the positive plates

of lead-acid batteries is well known to offer significant electrochemical improvements in

battery performance in respect of improved cycling and battery life.

A number of methods for controlling the tetra-basic lead sulphate crystals are also well

known in the literature. Simply heating the pasted plates during curing to more than 80

degC, for example during a short steam cure will generate a significant tetra-basic crystal

structure although with a wide ranging crystal size distribution, sizes of more than 50

microns being common. Therefore see figure 1 showing big sized tetra basic lead sulphate

crystals formed after a steam cure step using no seeding crystals or any other additives.

Figure 1

Presentation Ian Klein LABAT May 2008 PENOX GmbH Deutz-Muelheimer-Str. 173 51063 Cologne / Germany

Page 1


Another method, a so called in-situ method, uses the control of the temperature-time profile

in the paste mixer to generate a tetra-basic lead sulphate structure. One disadvantage of

this method is to control the crystal size, if not a special type of mixer is used.

One significant issue in creating the tetra-basic structure is to control the crystal size

distribution. Tetra-basic crystals, in comparison to tri-basic crystals, are much harder to

create. As the lead sulphate crystals develop there may be a limited number of developing

crystal seed sites due to a higher activation energy compared to tri-basic and hence it is

common to produce a relatively wide distribution across a plate with a number of very large

crystals. These larger tetra-basic crystals lead to problems in the later formation / charging

of the plates as evidenced by an increased specific energy consumption and extended

formation times when compared to tri-basic active materials.

The idea of ‘seeding’ the tetra-basic lead sulphate crystals as a means to control the growth

of these crystals is a well known technology. The principle is to add a powdered tetra-basic

lead sulphate crystal to the paste in the paste mixer. In this way a number of crystal seed

sites are created. This leads to a large number of relatively even tetra-basic lead sulphate

crystals. This technology is described in several patents.

The company Penox has long been a producer of lead oxides and also tri- and tetra-basic

lead sulphates for the plastic additives market. A development programme was started in-

house some 4 years ago to seed tetra-basic crystals in positive plates. This has lead to the

development of a specific patented tetra-basic product named TBLS+®.

Penox is now aware of a number of battery companies that are applying the product TBLS+®

or similar additives in their standard production process to control the crystal size.

During the last years Penox has worked with many battery companies world-wide in

applying this technology and this presentation describes some of the lessons learnt in

applying this very powerful seeding technology going from a research and development

product to a standard additive for many battery producers.


Page 2


Early Developments

Getting the Tetra-Basic Particle Size and Handling Right

The first trials carried out used tetra-basic lead sulphate as a powder with approx. 4 to 5

micron particle size, showed some benefits with an improvement in the homogeneity of the

crystal size distribution. The main means of generating the crystals has in general been the

heating of the pasted plates to more than 80 degC in a steam cure process. It has been

found that only a relatively short treatment of 1 to 2 hours is required to fully develop the

crystal structure.

However many plate samples showed evidence of larger crystals as analysed using

Scanning Electron Micrographs and in an effort to improve the distribution and minimise

these larger crystals with more than 50 micron length a more finely milled tetra-basic lead

sulphate powder with a particle size of approx. 2 to 3 microns was used.

Figure 2 is showing a tetra basic lead sulphate structure formed after a steam cure step

using 1 % of TTBLS powder with a particle size of approx. 5 micron as a seeding crystal. It

can be seen that there are again some bigger crystals in the active material.

Figure 2


Page 3


Again there were some improvements in the crystal distribution across the plates but not as

much as expected.

The following figure 3 shows a tetra basic lead sulphate structure again formed after a

steam cure step using 1 % of TTBLS powder with a particle size of 2 to 3 micron as a

seeding crystal with a few bigger sized crystals only.

Figure 3

In addition there were growing handling problems with such a fine dust, usually added

directly into the paste mixer. The generation of fine lead based dusts can lead to problems

with the blood lead levels of the workers and also it is possible that a significant fraction of

the seeding material is lost to the paste mixer exhaust system.

Building on Penox experience from the milling of organic powder pigments, a wet milled

slurry of tetra basic lead sulphate in water was tested. The wet milling process allows a very

fine controlled milling of the tetra basic crystals with particle sizes below one micron with

none of the dusting/hygiene issues of a powder. It was noticed that there was a strong

tendency of these finely milled particles to re-agglomerate after a time. Again, experience

from pigment processing indicated that a special type of silicic acid could be used to prevent

the re-agglomeration and this resulted in the Penox patent for TBLS+®.


Page 4


Graph 1 demonstrates the different particle size distribution curves of the above mentioned

types of tetra basic lead sulphate. The particle size curves are measured by using a laser

diffraction equipment.

0102030405060708090

100

0,1 0,6 1,2 2 4 10 20

Std. TTBLS

Finely milledTTBLSTBLS+

%

Micron

Graph 1

TBLS+® - Early Customer Trials and Production Process Development

Customer trials with TBLS+® very quickly showed benefits in the curing and formation in SLI

plate production related to process time reductions and energy savings.

The TBLS+® was added as approx. 1%, of the lead oxide content in the batch with a small

correction for the water addition in the paster, because the TBLS+® is a water based slurry

containing approx. 40% solids. The final crystal size of the plates can be controlled easily by

the amount of TBLS+® added to the paste batch as shown in the following pages (figures 4,

5 and 6).

Where figure 4 gives an idea about the tetra basic lead sulphate structure formed after a

steam cure step using 0.5 % of TBLS+® as a seeding crystal (the concentration that

performes very well for industrial batteries).


Page 5


Figure 4

Figure 5 shows again a tetra basic lead sulphate structure formed after a steam cure step

using 1.5 % of TBLS+® as seeding crystal. In most cases 1 to 1.5% TBLS+® are used for

SLI batteries.

Figure 5


Page 6


Finally figure 6 is showing a tetra basic lead sulphate structure formed after a steam cure

step using 3 % of TBLS+® as seeding crystal.

Figure 6

These trials showed for example that using a 1 hour steam cure for gravity casted grids a

very homogeneous tetra-basic crystal structure could be achieved. Following the steam cure

a short finishing cure was applied to reduce the free lead content before starting the final

drying. The excellent tetra basic crystal structure with no crystals bigger than 15 microns

and a good paste porosity, measured by mercury vapour penetration as shown in graph 2

for a Mercury porosimetry method result for the intrusion volume after 5 sec.

Graph 2


Page 7


lead to an almost 40% formation time reduction when compared to plates with larger

uncontrolled tetra-basic crystals.

These early trials supported the concept of the ‘continuous cure’ process – effectively

passing pasted plates through a temperature-humidity profiled tunnel in a continuous

process. A patented technology developed by the German company Muenstermann that

enables the battery producer to cure and dry their plates within 4 hours.

Since Penox produces the tetra-basic lead sulphate used to produce TBLS+®, several

production developments were introduced. Commercial tetra-basic lead sulphates as

produced in a wet batch process at high temperatures using litharge (PbO), water and

sulphuric acid are never 100% tetra-basic and may drop down to 60 or 80% with the

remainder being a mix of un-reacted PbO and tri-basic lead sulphate. During the wet milling

production process for TBLS+® it was noticed that the tetra-basic content could decrease.

This was found to be due to some un-reacted PbO inside the un-milled tetra-basic lead

sulphate being exposed during the milling process. In addition, the importance of a good pH

control was identified to ensure a long and stable shelf-life for TBLS+®.

TBLS+® - Large Scale Trials and Establishment as a Standard Additive

Over the past 3 years more then 30 full-scale plant trials for starter and industrial batteries

have been carried out across Europe, South America, United States and Asia. As a result of

these many trials there have been a number of areas where improvements in the application

of tetra-basic seeding have been made.

Paste Mixer

TBLS+® is best added after the oxide and water but before the acid addition. Adding the

TBLS+® slurry directly onto a dry oxide can lead to an inhomogeneous distribution and

therefore needs some additional mixing time to eliminate potential inhomogeneities. Adding

the TBLS+® after the water and oxide have been mixed leads to a well dispersed mix within

one or two minutes


Page 8


One area to watch for is over-filling of the paste mixer and general poor paste mixing. It has

been noted in some cases that efforts to improve the productivity have lead to increased

batch sizes in the mixer leading to some mixing problems that finally can result in greater

batch-to-batch variations of the paste plasticity and the paste density values.

Also it has been noticed that very often in the paste recipe the acid-oxide ratio has been

reduced to minimise the possibility of temperature spikes in the paster. These temperature

spikes can lead to uncontrolled tetra-basic crystal formation. With TBLS+® this is no longer

such a problem and it is common to increase acid-oxide ratios from 6 or 7 litres per 100kg

lead oxide up to 8 or 10 litres per 100kg lead oxide giving higher porosity values for the

paste and obviously reduces the work in the formation section. But these changes have to fit

into the electrical characteristics of the battery produced.

Curing and Drying

First plant trials with TBLS+® are usually without any changes to the existing process. This

establishes a base case or reference for further developments. A number of issues have

been identified with many current curing processes.

With large curing chambers, the pallets holding the plates can take a full day to load. During

this period a general loading temperature-humidity profile, in most cases the same as for the

curing operation, is used. However, due to the opening and closing of the doors and the

movements of the pallets the actual conditions inside the chamber can vary significantly.

The actual temperature-humidity profile experienced by the first pallets are very different to

the last pallet loaded. Likewise it can be observed that the free lead in the paste can start an

exothermic reaction and can sometimes dry out the plates especially if the more reactive mill

oxides are used.

During trials, Penox uses small data-loggers to check the actual temperature-humidity at

several points across the chamber and usually within a stack of plates. In many cases it is

noticed that the conditions in the chambers are very variable. This is often due to poor air

circulation within the chamber. Penox has worked with a number of chambers and has

developed a specific TBLS+® profile together with the Italian manufacturers CAM srl.


Page 9


TBLS+® treated plates in general are better able to cope with the above mentioned

problems in the curing chamber. However, it has been found that a short steam cure of 1 to

2 hours with more then 80 degC on the plates leads to a very well developed tetra-basic

crystal structure and helps to improve the adherence of the paste on the grid, especially if

the more corrosion resistant lead alloys are in use.

Thereafter, the plates are less sensitive to the secondary curing that was implemented to

speed up the free lead reduction. It has also found to be important to have a good air

circulation during the final drying to ensure the reaction of the small parts of residual free

lead.

The following two graphs are showing what savings are possible for the cure/dry operation.

Graph 3 compares the different ways of curing and drying of pasted plates.

0

5

10

15

20

25

Steaming 0 0 4 4 1

Lead reduction 0 0 0 8 1,5

Curing 20 24 16 0 0

Drying 16 12 12 6 1,5

Big Chamber -

3bas.

Big Chamber -

4bas.

Big Chamber

(with

CAM Chamber -

4bas.

Concure Process

Graph 3

The following graph 4 on the next page is giving a summary about possible savings in

percent by changing the curing/drying process as mentioned before.


Page 10


0,010,020,030,040,050,060,070,080,090,0

%

Big Chamber - 3bas. Plates

Big Chamber - 4bas. Plates

Big Chamber (with extra ...

CAM Chamber - 4bas. Plates

Concure Process

Savings in %

Graph 4

Formation

TBLS+® has been used in a number of different formation processes like air cooled; water

bath; acid recirculation. In general TBLS+® has shown very positive effects due to the very

much improved porosity of the plates. In general, TBLS+® provides much deeper pores

allowing a much better contact between the acid and the active material. Thanks to the

smaller sized tetra basic crystals the active material does not need so many resting periods

during the formation to allow the active material to relax. This was more important for the

large sized tetra basic crystals to prevent a reduction in the paste-grid adhesion.

Due to the improved formation characteristics of the positive plates treated with TBLS+®, it

has been noticed that some focus needs to be applied to the negative plate. Especially

during formation or charging, the negative plate can be fully charged well before the

positive, leading to heat and gassing in the final stages of the formation process.

It can be summarized that with the use of TBLS+® it is possible to achieve significant

savings in time and energy as shown next page in graph 5 and 6 for a 60 Ah OEM battery.


Page 11

PENOX GmbH

st TBLS+® Technology

Presentation Ian Klein LABAT May 2008

1 Edition

PENOX GmbH Deutz-Muelheimer-Str. 173 51063 Cologne / Germany

Page 12

0

200

400

600

Ah / Hours

Ford 60Ah, LB3

Std 4 bas. 52 7,75 450

TBLS+ 30,5 2 354,5

TBLS+ optimised 17,5 1 315

Time Resting Time

Ah

0,010,020,030,040,050,060,070,0

%

optimised

Std 4 bas. TBLS+ TBLS+

Savings for Battery type 60Ah, LB3

TimeEnergy

OEM Battery, 60 Ah, LB3

Graph 5

Graph 6

The best results are achieved using a formation process that was optimised for the small

sized tetra basic plates, in the graph 5 and 6 named optimised TBLS+®.

TBLS+® - Generating Plate Mass Reductions of 4 to 5%

A major outcome in the development of TBLS+® has been the need for a very close

cooperation with the customer. Some benefits such as improved curing and formation can

be achieved relatively quickly. However, by working through the battery production process

starting at the paste production and ending at the formation process can lead to additional

and very significant savings. This requires a very open and cooperative relationship, which

Penox has been fortunate enough to enjoy with several customers.

A number of processing issues in the battery production process have been identified

above. Many of these issues can be resolved or significantly improved with some limited

effort.


Once a good level of confidence has been established in the application of TBLS+® the next

step is to look at reducing the quantity of the active mass on the positive plate. The

significantly improved porosity of the plates means that much more of the active mass is

taking part in the electrochemical process. The active mass is reduced by small changes in

the paste recipe to reduce the paste density for example from 4.2 kg/litre to 4.0 kg/litre by

changing the acid/oxide ratio as previously mentioned.

The combined effect of a homogenous crystal structure with an uniform and high porosity

with good penetration of the acid into the active material provides an excellent positive plate

for the lead-acid battery. However, this work on improving the positive plate, traditionally one

of the major causes of battery failure, has indicated that the limiting factor in battery life

could now be the negative plate. Further work in this area has shown that adding TBLS+® to

the negative plates can significantly improve the porosity and permit a reduction in the plate

active mass. The following slides will show some results.

At first graph 7 is coming up with the Mercury-porosity measurement results of tri- and tetra

basic cured negative active material, where the intrusion volume of the tetra basic cured

paste is 4 times more than for the tri basic cured material.

Graph 7


Page 13


The following figure 7 is showing the crystal structure of a tetra basic cured negative plate.

Figure 7

Graph 8 shows the XRD patterns of negative active material with and without TBLS+®.

Graph 8


Page 14


But it must be stated that for the formation of tetra basic lead sulphate crystals there is a

need for some changes to the recipe of the negative active material especially for the

expander mixture and it has to be applied steam for a period of 3 hours to get a 100%

conversion into tetra basic crystals.

Not only does the application of TBLS+® permit active mass reductions to be made in both

plates but with the improved performance of the plates a re-evaluation of the basic battery

design is possible.

One Penox customer has been able to reconfigure the numbers of positive and negative

plates per cell leading to not only a lighter battery but with savings in grids as well as paste.

With the lead price at generally high levels this development is probably one of the most

significant means to reduce the costs of battery production as can be seen on the following

graph 9.

0

2

4

6

8

10

12

%

Std. design Std. design withTBLS+

Re-design withTBLS+

Savings in %

0

200

400

600

800

1000

k€

Std. design Std. design Re-design with

Savings in k€/Mio Batteries

with TBLS+ TBLS+

Lead price1,200 €/tonLead price1,800 €/tonLead price2,300 €/ton

Graph 9


Page 15


Remarks:

All SEM pictures shown in this paper have a magnitude of 1,000x. The XRD and Mercury

Porosity Measurement were analysed by H.C. Starck GmbH, Goslar Germany.

References:

Bode Lead-Acid Batteries

Schwinhorst, Nitsche Method for Producing, Maturing and Drying Negative and

Positive Plates for Lead Accumulators (WO 2006/128621)

Nitsche, Klein Additive for Producing a Positive Active Material for Lead-Acid

Storage Batteries, a Method for its Production and a Method

for its use (EP 1576679)

Nitsche, Lahme Curing of Positive Plates (EP 1235287)

Boden, Labovitz Battery Paste Additive and Method for Producing Battery

Plates (WO 2005/094501)

Meyer Paste Curing Additive (WO 2006/034466)


Page 16

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