EP4008032A1 - Method for producing lead acid batteries - Google Patents

Method for producing lead acid batteries

Info

Publication number
EP4008032A1
EP4008032A1 EP20726336.9A EP20726336A EP4008032A1 EP 4008032 A1 EP4008032 A1 EP 4008032A1 EP 20726336 A EP20726336 A EP 20726336A EP 4008032 A1 EP4008032 A1 EP 4008032A1
Authority
EP
European Patent Office
Prior art keywords
zeolites
batteries
silicates
sulfuric acid
alkaline
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20726336.9A
Other languages
German (de)
French (fr)
Inventor
Werner Nitsche
Charles Robert Sullivan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Crs Tech GmbH
Eng Office Dr Nitsche Ltd
Engineering Office Dr Nitsche Ltd
Original Assignee
Crs Tech GmbH
Eng Office Dr Nitsche Ltd
Engineering Office Dr Nitsche Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Crs Tech GmbH, Eng Office Dr Nitsche Ltd, Engineering Office Dr Nitsche Ltd filed Critical Crs Tech GmbH
Priority claimed from PCT/EP2020/063137 external-priority patent/WO2020244891A1/en
Publication of EP4008032A1 publication Critical patent/EP4008032A1/en
Pending legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/06—Lead-acid accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/06—Lead-acid accumulators
    • H01M10/08—Selection of materials as electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/06—Lead-acid accumulators
    • H01M10/12—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/14—Electrodes for lead-acid accumulators
    • H01M4/16—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/14—Electrodes for lead-acid accumulators
    • H01M4/16—Processes of manufacture
    • H01M4/20—Processes of manufacture of pasted electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0002—Aqueous electrolytes
    • H01M2300/0005—Acid electrolytes
    • H01M2300/0011—Sulfuric acid-based
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • Lead acid batteries exhibit positive and negative electrodes separated by ion permeable separators.
  • the electrodes are produced from lead grids filled with a lead paste produced from leady oxide, sulfuric acid, water and some additives.
  • organic or inorganic fibers and sometimes seeding crystals are added.
  • organic lignin-compounds barium sulphate, carbon compounds and also binding fibers are used.
  • lead grids gravity cast, expanded metal, punched or continuously casted produced lead alloys using small amounts of calcium, tin, aluminum or antimony are used.
  • the paste used to cover the lead grid for the positive electrode will be compounded from lead oxide of PbO with a remaining Pb content of about 20 - 30%, water, sulfuric acid and synthetic fibers in a purpose-built oxide mixer to ensure a homogenous distribution and bonding of the various ingredients.
  • the pasted plates undergo in a curing process a heat and steam treatment to initiate a chemical process to obtain a 3-basic and/or 4-basic lead sulphate structure as well as a reduction of Pb from leady oxide to PbO and thereby reducing the Pb (“free lead”) content.
  • the PbO helps to link the 3- and/or 4- basic lead sulphate crystals to obtain a stable network of crystals.
  • the pasted plates will be dried.
  • lignin sulphates normally prevent the nucleation to 4-basic lead sulphate in temperatures above 80°C. However, when steam is applied, the crystal growth is finished within 1 hour.
  • the manufactured plates are made into electrodes in the formation step.
  • the basic lead sulphate and PbO are converted to Pb and for the positive electrodes, to lead dioxide PbC>2.
  • the formation was done directly after the curing process, by placing the electrodes in external containers.
  • the formation is generally done after assembling of the plates in the final battery containers.
  • the positive and negative plates are separated by an ion permeable polyethylene or fiber glass mat sheet (“separator”) in the cells of the container. Less common also PVC separators are used.
  • automotive 12 volt lead acid batteries were mainly used for cranking and lighting in motor vehicles or in industrial applications as stationary power supplies or for traction purposes, e.g. fork lifters.
  • the design of industrial batteries is different to automotive batteries.
  • micro-hybrid engine technologies A new application is coming into use in micro-hybrid engine technologies.
  • the battery supplies energy to assist acceleration and is re-charged from the combustion engine but also from energy derived from braking. This creates the need for a very fast re-chargeability and long cycle life.
  • driverless transportation becomes more prevalent, the reliability of the battery will take on a crucial importance in terms of safety.
  • the drive train is powered primarily by a battery, which is charged by an internal combustion engine.
  • the 48 volt battery, powering the electrical drive of a mild hybrid engine needs a fast rechargeability and greatly increased cycling capability as compared to that which is currently available from lead acid batteries.
  • the electrical drive has an energy efficiency of about 90% compared to ⁇ 50% of diesel-powered internal combustion engines and especially ⁇ 40% of petrol engines.
  • the combustion engine is able to run at an optimized speed, greatly reducing energy consumption as well as greatly reducing the creation of polluting nitrogen oxide, especially in urban areas.
  • possibilities for 48 Volt lead acid battery systems exist for alternative energy systems, including solar power, in order to provide off-peak energy.
  • lithium ion batteries are favored for 48 Volt applications due to the greater cycle life and faster
  • Lead acid batteries function best in a partial state of charge, between 100% fully charged and 50% discharged. Modern vehicles as well as alternative energy applications need to function reliably at deeper discharge states and deliver increasing numbers of cycles to provide electrical power over time. Mild-hybrid applications demand for better charge acceptance and recharge performance than available in lead acid batteries available currently. Especially for mild-hybrid applications in modern vehicles, the less expensive, better recyclable lead acid batteries can only become an alternative to lithium ion batteries, if the recharge performance and the number of cycles achieved can be improved significantly.
  • lead acid batteries The recharging of lead acid batteries is done by voltage limited alternators set to about 14.4 V for modern lead calcium or pure lead batteries. During discharge lead sulphate is created and must be reversed to lead and lead dioxide to recharge the lead acid batteries:
  • the voltage DE is given by
  • V AE 2.041 V + 0.059 lg ⁇ a H2S0 J a Hz0 ) V (4) being the sum of the positive and negative electrode and mainly depending on the activity of the sulfuric acid in the pores of the electrodes. In case the voltage AE equals the applied voltage of the alternator, the current drops down.
  • the voltage control becomes active and the current is adjusted down to keep the set voltage constant.
  • the recharge time is limited, which often means that the battery cannot be recharged completely during the applied recharge time.
  • lead sulphate PbSC is formed (“sulfation”) on the positive as well as negative electrodes. Both electrodes gain from cycle to cycle an increasing amount of lead sulphate PbSC . More and more former 4- or in particular 3-basic cured crystals of the positive electrodes become fully PbSC crystals and lose their contact to the electrode. Over time the PbS04 crystals completely dislodge from the plate or become very soft with low contact to the plate. On the other hand, the PbS04 crystals on the negative electrodes become very hard and insoluble, blocking the electrochemical exchange. Due to this process the electrochemical activity diminishes which reduces the possible achievable cycles and thereby the lifetime of the battery.
  • VRLA valve regulated lead acid
  • the negative electrode will be recharged faster than the positive. In this case, close to reaching 14.4 volts (the charger voltage), the positive electrode starts oxygen evolution before the negative electrode is fully recharged. Locally, inside the pores of the positive plates, the specific gravity of the H2O/H2SO4 electrolyte mixture will increase during recharge to more than 1.5 g/cm 3 due to the production of sulphate ions and decrease of water. In the VRLA battery, the oxygen will pass the partially filled glass mat and oxidizes lead at the negative electrode. This resulting PbO will discharge the negative electrode and create PbSC>4. Due to this effect, called recombination, both electrodes will be recharged much more fully.
  • the minimum pore size is limited by the glass mat fibers able to be produced. Moreover, the smaller the fibers the more expensive is the glass mat. By compressing the glass mat a further reduction of the glass mat pores is possible to increase the capillary force. In practical application, it can be found that the cycle number is proportional to the compression. The higher the compression is, the higher is the cycle number. However, on the other hand, the free volume for acid is decreased by increasing compression of the glass mat, which reduces the capacity of the battery. Therefore, in practical applications
  • compressions of up to 80 kpa are used to optimize the trade-off between capillary action and acid availability.
  • GEL VRLA batteries are in use.
  • jelly silica containing small cracks is used to obtain the effects of capillary force to promote recombination (1 above) and the exchange of water and ions (2 above). Both battery types show better cycle performance compared to flooded batteries.
  • GEL-batteries But the internal resistance of GEL-batteries is higher than in flooded batteries due to the jelly silica and the use of traditional polyethylene battery separators. As a result, GEL batteries are not well suited for applications with limited recharge time, such as automotive applications. This can be shown in the 50% DoD and 17.5% DoD cycle life test mentioned above.
  • the jelly silica as well as the traditional separators slow down the ion exchange of the electrodes.
  • silica compounds have been tested so far with respect to increase the capacity as well as cold cranking performance of lead acid batteries.
  • the silica is used to create cavities inside the electrode to increase the amount of acid inside the electrodes and to achieve increased gates for ions to penetrate the electrodes. The effects are observable but not of commercial interest up to now.
  • the above task is solved with a method for producing lead acid batteries, which is characterized in that alkaline silicates and/or alkaline zeolites, with cavities and rough surface originated from agglomeration, are added to the sulfuric acid or during the manufacturing of the positive active material for the lead acid batteries to reduce the Nernst voltage DE related to the activity of the sulfuric acid during recharge.
  • alkaline silicates or alkaline zeolites e.g.
  • sodium alumina silicates or alternatively potassium aluminum silicates added to the acid or the paste of lead acid batteries during production improve dramatically the recharge performance of the batteries and thereby also the cycle life. The effect is triggered by the chemical’s cavities and rough surface formed by agglomeration.
  • Especially sodium or potassium aluminum silicates produced under agglomeration are capable to absorb sulphate ions at their surface and especially in the pores at higher sulphate concentrations and release them as the sulphate concentration decreases. Due to this property, the adsorption decreases the activity of the sulfuric acid in relation to the absence of silicates or zeoliths.
  • These materials will be defined as activity blocker in the following context of the activity of sulfuric acid according to equation (4). More specifically, the positive charge of the alkaline ions favors the binding of the sulphate ions and lowers the activity inside the electrodes. Metal oxides and activated carbons appear to absorb sulphate ions also, thereby reducing the activity of sulfuric acid.
  • the adsorption of sulphate ions is depending on the concentration of the sulfuric acid. For a concentration > 1.4 g/cm 3 the adsorption becomes significant and slows down the increase of the sulphate ion activity.
  • the voltage DE is increasing more slowly and the current in constant voltage recharge is kept for a longer time at the set value compared with batteries without adding the above-mentioned silicates and/or zeolites.
  • This invention is especially significant for all applications requiring long cycle life under discharge followed by full recharge conditions, including batteries for mild hybrid engines as well as batteries requiring a long cycle life under partial state of charge conditions, such as start stop engines.
  • the invention improves the charge acceptance of lead acid batteries.
  • the activity blocker In case of adding the activity blocker into the sulfuric acid, the activity blocker will be homogeneously distributed in the acid. Usually the activity blocker in and close to the surface of the positive and partly in the negative plate has influence on the voltage A E during recharge. The activity is blocked only inside the electrodes, where the sulfuric acid gravity significantly exceeds specific gravities of more than 1.5 g/cm 3 during recharge and the voltage DE increases to 14.4 V. With respect to the 17.5% DoD test, significantly positive results are achieved with the activity blocker added to the electrolyte. A performance improvement of 4 times higher cycle number compared to the same design of batteries without the activity blocker is achieved, with none of the negative side effects as occurring with other known additives, such as carbon or metal oxide additives.
  • AGM lead acid batteries for mild hybrid applications instead of much more expensive, non-recyclable, unsafe lithium-ion batteries.
  • All batteries requiring a long cycle life with deep discharge/recharge regimens, including absorbent glass mat (AGM) batteries for mild hybrid vehicles will benefit from this invention.
  • batteries subject to high numbers of discharge/recharge cycles, such as start stop will greatly benefit from using the activity blocker.
  • This invention is the key to allow for low cost no emission vehicles for low speed applications in the metropoles of developing countries.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Cell Separators (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

Under constant voltage recharge, as occurs in battery applications, the recharge current drops if the Nernst voltage equals the applied voltage. Therefore, lead acid batteries cannot achieve optimal cycle life or rechargeability. The main reason is the increase of the Nernst voltage due to build-up of the specific gravity of the sulfuric acid, which increases more quickly in the positive electrode than in the negative electrode. The invention shows that specific alkaline silicates and/or alkaline zeolites act as blocker of the quick increase in sulfuric acid activity in the positive electrode. This is due to the fact that the cavities and alkaline atoms capture the sulphate ions and thereby reduce the sulfuric acid activity. Especially highly agglomerated alkaline aluminum silicates and alkaline aluminum zeolites are of special interest.

Description

Specification:
Method for producing lead acid batteries
State of the art:
Lead acid batteries exhibit positive and negative electrodes separated by ion permeable separators. The electrodes are produced from lead grids filled with a lead paste produced from leady oxide, sulfuric acid, water and some additives.
For positive electrodes organic or inorganic fibers and sometimes seeding crystals are added. For negative electrodes organic lignin-compounds, barium sulphate, carbon compounds and also binding fibers are used. For the lead grids, gravity cast, expanded metal, punched or continuously casted produced lead alloys using small amounts of calcium, tin, aluminum or antimony are used.
The paste used to cover the lead grid for the positive electrode will be compounded from lead oxide of PbO with a remaining Pb content of about 20 - 30%, water, sulfuric acid and synthetic fibers in a purpose-built oxide mixer to ensure a homogenous distribution and bonding of the various ingredients.
To achieve a high porosity, the pasted plates undergo in a curing process a heat and steam treatment to initiate a chemical process to obtain a 3-basic and/or 4-basic lead sulphate structure as well as a reduction of Pb from leady oxide to PbO and thereby reducing the Pb (“free lead”) content. The PbO helps to link the 3- and/or 4- basic lead sulphate crystals to obtain a stable network of crystals. At the end of the process, the pasted plates will be dried.
To achieve a 4-basic lead sulphate crystal structure temperatures of > 80°C are necessary during the curing process. On the other hand, to achieve a 3-basic crystal structure the temperature should not exceed 60°C to avoid the appearance of 4- basic lead sulphate crystals. The crystal growth takes only 1 to 2 hours for temperatures > 80°C but takes >12 hours for temperatures less than 60°C. Positive electrodes made from 4-basic lead sulphate show better performance in case of deeper discharge and longer cycle numbers compared to positive electrodes made from 3-basic lead sulphate.
To create the negative paste, leady oxide, sulfuric acid, water, fibres, lignin compounds, barium sulphate and carbon compounds are combined and mixed in the oxide mixer. The lignin sulphates normally prevent the nucleation to 4-basic lead sulphate in temperatures above 80°C. However, when steam is applied, the crystal growth is finished within 1 hour.
Following plate curing, the manufactured plates are made into electrodes in the formation step. For the negative electrodes, the basic lead sulphate and PbO are converted to Pb and for the positive electrodes, to lead dioxide PbC>2. In the past, the formation was done directly after the curing process, by placing the electrodes in external containers. Currently, for environmental and cost reasons, the formation is generally done after assembling of the plates in the final battery containers. The positive and negative plates are separated by an ion permeable polyethylene or fiber glass mat sheet (“separator”) in the cells of the container. Less common also PVC separators are used.
Definition of task:
In the past, automotive 12 volt lead acid batteries were mainly used for cranking and lighting in motor vehicles or in industrial applications as stationary power supplies or for traction purposes, e.g. fork lifters. The design of industrial batteries is different to automotive batteries.
Today, lead acid batteries are used in motor vehicles with an increased number of electrical consumers. The demands on the 12 volt battery, in terms of the number of charge-discharge cycles necessary prior to replacement, has greatly increased due to the CO2 saving start-stop engine technology. By switching off the engine at each stop of more than a few seconds, the number of charge-discharge cycles has dramatically increased.
A new application is coming into use in micro-hybrid engine technologies. In micro hybrid engines, the battery supplies energy to assist acceleration and is re-charged from the combustion engine but also from energy derived from braking. This creates the need for a very fast re-chargeability and long cycle life. Furthermore, as driverless transportation becomes more prevalent, the reliability of the battery will take on a crucial importance in terms of safety.
In the future, a quantum leap forward will be needed to support mild hybrid engine systems. In mild hybrid engine systems, the drive train is powered primarily by a battery, which is charged by an internal combustion engine. The 48 volt battery, powering the electrical drive of a mild hybrid engine needs a fast rechargeability and greatly increased cycling capability as compared to that which is currently available from lead acid batteries. The electrical drive has an energy efficiency of about 90% compared to < 50% of diesel-powered internal combustion engines and especially < 40% of petrol engines. By channeling the energy from the internal combustion engine to the electric motor, the combustion engine is able to run at an optimized speed, greatly reducing energy consumption as well as greatly reducing the creation of polluting nitrogen oxide, especially in urban areas. In addition, possibilities for 48 Volt lead acid battery systems exist for alternative energy systems, including solar power, in order to provide off-peak energy. Currently, lithium ion batteries are favored for 48 Volt applications due to the greater cycle life and faster
rechargeability, although lead acid technology is safer, cheaper and does not have the end of use recycling problems of lithium batteries. The cost for the lithium battery is widely recognized as the biggest reason for the lack of purchase and use of full electrical and electrical hybrid vehicles.
Lead acid batteries function best in a partial state of charge, between 100% fully charged and 50% discharged. Modern vehicles as well as alternative energy applications need to function reliably at deeper discharge states and deliver increasing numbers of cycles to provide electrical power over time. Mild-hybrid applications demand for better charge acceptance and recharge performance than available in lead acid batteries available currently. Especially for mild-hybrid applications in modern vehicles, the less expensive, better recyclable lead acid batteries can only become an alternative to lithium ion batteries, if the recharge performance and the number of cycles achieved can be improved significantly.
The recharging of lead acid batteries is done by voltage limited alternators set to about 14.4 V for modern lead calcium or pure lead batteries. During discharge lead sulphate is created and must be reversed to lead and lead dioxide to recharge the lead acid batteries:
The chemical reactions are described below. charged state ¾ discharged state
Pb + Pb02 + 2 H2S04 ¾ 2 PbS04 + 2 H20 (1) positive electrode:
PbS04 + 2 H20 ¾ Pb02 + H2S04 + 2 H+ + 2 e~ (2) negative electrode:
PbS04 + 2 e ¾ Pb + S0 (3)
The voltage DE is given by
AE = 2.041 V + 0.059 lg{aH2S0J aHz0) V (4) being the sum of the positive and negative electrode and mainly depending on the activity of the sulfuric acid in the pores of the electrodes. In case the voltage AE equals the applied voltage of the alternator, the current drops down.
During recharge sulphate ions are going in solution in the pores of the positive and negative electrode according to equations (2) and (3). Additional water is departed into ions in the pores of the positive electrode increasing the concentration and activity in the positive electrode more than in the negative electrode and therefore increasing the voltage AE. An exchange of sulphate ions to the reservoir and reflow of water occurs caused only by diffusion processes. This process takes time, which is a growing problem because in modern applications, discharge and recharge follow each other in shorter and shorter time intervals.
To recharge lead acid batteries, chargers with voltage control are normally in use.
As soon as the voltage DE equals the applied voltage of the charger, the voltage control becomes active and the current is adjusted down to keep the set voltage constant. In most applications, the recharge time is limited, which often means that the battery cannot be recharged completely during the applied recharge time.
Due to the incomplete recharge of the positive electrode, lead sulphate PbSC is formed (“sulfation”) on the positive as well as negative electrodes. Both electrodes gain from cycle to cycle an increasing amount of lead sulphate PbSC . More and more former 4- or in particular 3-basic cured crystals of the positive electrodes become fully PbSC crystals and lose their contact to the electrode. Over time the PbS04 crystals completely dislodge from the plate or become very soft with low contact to the plate. On the other hand, the PbS04 crystals on the negative electrodes become very hard and insoluble, blocking the electrochemical exchange. Due to this process the electrochemical activity diminishes which reduces the possible achievable cycles and thereby the lifetime of the battery.
The type of battery most likely to be able to achieve the higher number of cycles and rechargeability needed for modern vehicles, is the valve regulated lead acid (VRLA) batteries which use fiber glass mat as a separator to trap the electrolyte acid. VRLA batteries exhibit a better charge acceptance compared to flooded lead acid batteries, in which the electrolyte flows freely in and around the electrodes.
Two major effects are the reason for the better recharge capability:
(1 ) The negative electrode will be recharged faster than the positive. In this case, close to reaching 14.4 volts (the charger voltage), the positive electrode starts oxygen evolution before the negative electrode is fully recharged. Locally, inside the pores of the positive plates, the specific gravity of the H2O/H2SO4 electrolyte mixture will increase during recharge to more than 1.5 g/cm3 due to the production of sulphate ions and decrease of water. In the VRLA battery, the oxygen will pass the partially filled glass mat and oxidizes lead at the negative electrode. This resulting PbO will discharge the negative electrode and create PbSC>4. Due to this effect, called recombination, both electrodes will be recharged much more fully. For flooded batteries, the oxygen escapes to the surface, preventing the positive plate from fully charging. Therefore, from cycle to cycle the battery cannot be fully recharged and sulfation occurs. This can be shown in the standardized“50% DoD” charge- discharge test, in which the capability to recharge to 100% after a 50% discharge is tested.
(2) To check the performance of recharge capability during normal cycles in applications, the“17.5% DoD” charge-discharge test was created. In this test, the battery will be discharged to 50% followed by 40 minutes recharge with 7 times the rated capacity 120 and 30 minutes discharge with 7 times the rated capacity but also limiting the voltage to 14.4 volts and 14.0 volts at 60°C, respectively. This test is quite close to practical application of batteries with normal internal combustion engines to check the recharge performance. For this test, the capability of sulphate ion and water between the electrode pores and the acid reservoir between the electrodes is important. For VRLA batteries the glass mat separator exhibits a capillary force on the ions and the water and supports the exchange of water and ions.
During recharge, sulphate ions will be produced in both electrodes and increases the voltage DE, thereby reducing the recharge current if it equals the applied charger voltage. The capillary force supports the ion and water exchange and therefore keeps the voltage AE lower compared to normal flooded batteries with no capillary forces. The smaller the pores of the glass mat, the stronger the capillary force.
In commercial VRLA batteries the minimum pore size is limited by the glass mat fibers able to be produced. Moreover, the smaller the fibers the more expensive is the glass mat. By compressing the glass mat a further reduction of the glass mat pores is possible to increase the capillary force. In practical application, it can be found that the cycle number is proportional to the compression. The higher the compression is, the higher is the cycle number. However, on the other hand, the free volume for acid is decreased by increasing compression of the glass mat, which reduces the capacity of the battery. Therefore, in practical applications
compressions of up to 80 kpa are used to optimize the trade-off between capillary action and acid availability. Besides VRLA batteries with glass mat, GEL VRLA batteries are in use. In this case, jelly silica containing small cracks is used to obtain the effects of capillary force to promote recombination (1 above) and the exchange of water and ions (2 above). Both battery types show better cycle performance compared to flooded batteries.
But the internal resistance of GEL-batteries is higher than in flooded batteries due to the jelly silica and the use of traditional polyethylene battery separators. As a result, GEL batteries are not well suited for applications with limited recharge time, such as automotive applications. This can be shown in the 50% DoD and 17.5% DoD cycle life test mentioned above. The jelly silica as well as the traditional separators slow down the ion exchange of the electrodes.
In addition, additives have been introduced recently to increase cycle life. Carbon has been extensively tested recently, both as a paste additive and in solid form as a negative electrode. While cycle life has been increased by a factor of 2x to 4x, the additive greatly increases the rate of hydrogen evolution, resulting in unacceptable water loss and accelerated corrosion of the positive grid.
Several silica compounds have been tested so far with respect to increase the capacity as well as cold cranking performance of lead acid batteries. The silica is used to create cavities inside the electrode to increase the amount of acid inside the electrodes and to achieve increased gates for ions to penetrate the electrodes. The effects are observable but not of commercial interest up to now.
Invention:
According to the invention, the above task is solved with a method for producing lead acid batteries, which is characterized in that alkaline silicates and/or alkaline zeolites, with cavities and rough surface originated from agglomeration, are added to the sulfuric acid or during the manufacturing of the positive active material for the lead acid batteries to reduce the Nernst voltage DE related to the activity of the sulfuric acid during recharge.
Further embodiments of the invention are specified in the dependent claims. Within this invention a new approach is followed to use silica and/or zeolites to improve the recharge performance of lead acid batteries. Crystalline alkali silicates or alkali zeolites form a group of framework silicates known for reversible water and alkaline ions exchange capability. From the alkali elements lithium, sodium, potassium, rubidium, cesium and francium special interest is focused on sodium and potassium because of its wide-spread industrial use, however all these elements will function.
In this invention, it is discovered that alkaline silicates or alkaline zeolites, e.g.
sodium alumina silicates or alternatively potassium aluminum silicates, added to the acid or the paste of lead acid batteries during production improve dramatically the recharge performance of the batteries and thereby also the cycle life. The effect is triggered by the chemical’s cavities and rough surface formed by agglomeration.
Especially sodium or potassium aluminum silicates produced under agglomeration are capable to absorb sulphate ions at their surface and especially in the pores at higher sulphate concentrations and release them as the sulphate concentration decreases. Due to this property, the adsorption decreases the activity of the sulfuric acid in relation to the absence of silicates or zeoliths. These materials will be defined as activity blocker in the following context of the activity of sulfuric acid according to equation (4). More specifically, the positive charge of the alkaline ions favors the binding of the sulphate ions and lowers the activity inside the electrodes. Metal oxides and activated carbons appear to absorb sulphate ions also, thereby reducing the activity of sulfuric acid. However, metal oxide and activated carbon have been shown to reduce the overvoltage and thereby accelerate water loss, which is not acceptable for modern maintenance free batteries. Also, activated carbon will be oxidized by the high oxidation potential of PbC>2 and therefore being destroyed. Therefore, carbon compounds are of short-lived usefulness.
As mentioned before, the adsorption of sulphate ions is depending on the concentration of the sulfuric acid. For a concentration > 1.4 g/cm3 the adsorption becomes significant and slows down the increase of the sulphate ion activity.
Therefore, the voltage DE is increasing more slowly and the current in constant voltage recharge is kept for a longer time at the set value compared with batteries without adding the above-mentioned silicates and/or zeolites. This invention is especially significant for all applications requiring long cycle life under discharge followed by full recharge conditions, including batteries for mild hybrid engines as well as batteries requiring a long cycle life under partial state of charge conditions, such as start stop engines. The invention improves the charge acceptance of lead acid batteries.
For testing the capability of batteries for the start and stop engine application the above-mentioned 17.5% DoD test is in use. It could be proved that for batteries more than 2000 cycles could be achieved for flooded batteries with sodium aluminum silicate compared to batteries of the same production without this silicate only achieving 500 - 600 cycles. The adsorption of the sulphate ions is depending on the concentration of the sulfuric acid as mentioned above. While some deterioration in cold cranking performance has been observed, it is marginal and does not hinder fulfilling the requirements for cranking power. The rated capacity is not affected because at sulfuric acid concentrations below about 1.15 g/cm3 which equals the cut-off voltage for capacity tests, because during discharge the activity is not affected by the mentioned alkaline silicates. This is due because the forming of lead sulphate is stronger than the adsorption to the silicates or zeolites.
Specifically, for AGM batteries with a compression of typically 50 - 60 kpa more than 5000 cycles could be obtained in the 17.5% DoD test compared to 1600 - 1800 without addition.
Tests have shown that the activity blocker can be added to the sulfuric acid as well as to the lead oxide in the paste mixing process.
1. Addition to the electrolyte sulfuric acid:
In case of adding the activity blocker into the sulfuric acid, the activity blocker will be homogeneously distributed in the acid. Mostly the activity blocker in and close to the surface of the positive and partly in the negative plate has influence on the voltage A E during recharge. The activity is blocked only inside the electrodes, where the sulfuric acid gravity significantly exceeds specific gravities of more than 1.5 g/cm3 during recharge and the voltage DE increases to 14.4 V. With respect to the 17.5% DoD test, significantly positive results are achieved with the activity blocker added to the electrolyte. A performance improvement of 4 times higher cycle number compared to the same design of batteries without the activity blocker is achieved, with none of the negative side effects as occurring with other known additives, such as carbon or metal oxide additives. This effect will be achieved starting over 2% total acid weight. An increase in cycle life can be achieved by adding a higher weight % of alkaline silicates to the sulfuric acid. Of special interest is 4% weight to 15% weight in relation to the sulfuric acid weight of the battery cell.
In case of absorbent glass mat (AGM) batteries with low compression of 10 - 20 kpa, which achieve normally only 600 - 800 cycles, similar cycle number as for batteries with 50 - 60 kpa without activity blocker were obtained. This is of interest for battery producers without an expensive assembly machine, needed to
manufacture AGM batteries with compression. In addition, a relatively expensive battery container with enforced outside walls would not be required. This will give such manufacturers the capability to produce inexpensive batteries for start stop applications.
2. Addition of the activity blocker during positive paste preparation:
It is of advantage to add the activity blocker only during preparation of the positive active material. In this case less than one-third of the weight of activity blocker, e.g. sodium aluminum silica, is necessary to gain the same performance as necessary to be added to the sulfuric acid.
(1 ) 3-basic lead sulphate: No specific requirements are necessary except that more water than normal may be required because the activity blocker will absorb water to fill the pores. In any case it is of advantage to solve the activity blocker first in water before adding it into the paste mixer.
(2) 4-basic lead sulphate: It will be best to add first oxide, seeds, fibers, and water to the mixer. Afterwards it is of advantage to add the prior prepared activity blocker and mix it for a couple of minutes to achieve a homogenous distribution. The activity blocker is almost entirely insoluble and will stay in the positive electrode, because it is prevented from leaking out due to the huge size of the agglomerates inside the porous positive electrode.
The recharge performance due to blocking the activity of the sulfuric acid will reduce the Nernst voltage DE and keep the recharge for a longer time higher. Tests did show that by use of activity blocker an increase of the cycle number for the 17.5% DoD test of a factor > 4 was obtained.
This significant increase will allow the use of AGM lead acid batteries for mild hybrid applications instead of much more expensive, non-recyclable, unsafe lithium-ion batteries. All batteries requiring a long cycle life with deep discharge/recharge regimens, including absorbent glass mat (AGM) batteries for mild hybrid vehicles will benefit from this invention. In addition, batteries subject to high numbers of discharge/recharge cycles, such as start stop, will greatly benefit from using the activity blocker. This invention is the key to allow for low cost no emission vehicles for low speed applications in the metropoles of developing countries.

Claims

Claims:
1. Method for producing lead acid batteries,
characterized in that
alkaline silicates and/or alkaline zeolites, with cavities and rough surface originated from agglomeration, are added to the sulfuric acid or during the manufacturing of the positive active material for the lead acid batteries to reduce the Nernst voltage DE related to the activity of the sulfuric acid during recharge.
2. Method according to claim 1 , characterized in that sodium aluminum
silicates, potassium aluminum silicates, sodium aluminum zeolites or potassium aluminum zeolites are added to the sulfuric acid or to the positive active material of the lead acid batteries to reduce the activity of the sulfuric acid.
3. Method according to claim 2, characterized in that sodium aluminum
silicates, potassium aluminum silicates, sodium aluminum zeolites or potassium aluminum zeolites are added with a weight percentage of > 2% weight with respect to the sulfuric acid.
4. Method according to claim 3, characterized in that sodium aluminum
silicates, potassium aluminum silicates, sodium aluminum zeolites or potassium aluminum zeolites are added with a weight percentage of 4 - 8 % weight with respect to the sulfuric acid for enhanced flooded battery (EFB battery) applications.
5. Method according to claim 2, characterized in that sodium aluminum
silicates, potassium aluminum silicates, sodium aluminum zeolites or potassium aluminum zeolites are added with a weight percentage of > 0.67% to the amount of leady oxide to the positive active material.
6. Method according to claim 5, characterized in that sodium aluminum silicates, potassium aluminum silicates, sodium aluminum zeolites or potassium aluminum zeolites are added with a weight percentage of 1 - 2 % to the amount of leady oxide to the positive active material.
7. Method according to claim 1 , characterized in that sodium aluminum
silicates, potassium aluminum silicates, sodium aluminum zeolites or potassium aluminum zeolites are used for manufacturing of absorbent glass mat (AGM) batteries with low compression < 10 kpa.
8. Method according to claim 1 , characterized in that sodium aluminum
silicates, potassium aluminum silicates, sodium aluminum zeolites or potassium aluminum zeolites are added to absorbent glass mat (AGM) batteries for mild hybrid applications with a weight percentage of > 4% to the amount of leady oxide to the positive active material.
EP20726336.9A 2019-06-05 2020-05-12 Method for producing lead acid batteries Pending EP4008032A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IES20190083 2019-06-05
PCT/EP2020/063137 WO2020244891A1 (en) 2019-06-05 2020-05-12 Method for producing lead acid batteries

Publications (1)

Publication Number Publication Date
EP4008032A1 true EP4008032A1 (en) 2022-06-08

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EP (1) EP4008032A1 (en)

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