Origins of lead acid battery life
It is true to say that batteries are one of the major innovations which have combined with other technologies to shape the modern industrial world. From industrial to domestic to personal use, they have truly given us freedoms and possibilities which would be impossible without portable and stationary energy storage.
It is very clear to any modern human, that the march of the battery into more and more aspects of our daily lives is on a rapid increase, from single-cell- single-use in handheld devices like an AA alkaline for a computer mouse or a zinc-air button cell used in a wristwatch, to a grid-scale megawatt Battery Energy Storage System (BESS). Despite this plethora of chemistries and applications, it is the lead acid battery chemistry which is still, after 160 years since its invention, the most prolific provider of stored energy on the planet. Fig. 1 shows the breakdown of battery sales by type and MWh sold over the last 27 years
This comes as a surprise to some who think that li-ion is the highest-selling technology. This is true but only in value, not in, capacity. Because of its higher cost per kWh, Lithium-ion battery has a higher sales value and bigger revenue than lead acid. However, this is one of the reasons that the lead acid batteries (LAB) has endured so long in a highly competitive and changing commercial environment.
In this blog, we look at the invention of the lead acid batteries – an electrochemical storage battery, and trace its origins through history, from the first known examples of electrochemical cells through to the modern VRLA and bipolar versions.
In 1749, Benjamin Franklin, the U.S. polymath, first used the term “battery” to describe a set of linked capacitors he used for his experiments with electricity. These capacitors were panels of glass coated with metal on each surface. These capacitors were charged with a static generator and discharged by touching metal to their electrode. Linking them together in a “battery” gave a stronger discharge. Originally having the generic meaning of “a group of two or more similar objects functioning together”, as in an artillery battery, the term was used for voltaic piles and similar devices in which many electrochemical cells were connected together.
The lead acid battery is an electrochemical storage device and as such has the same principle of providing an electric current and voltage as all other electrochemical batteries, some of which preceded the adoption of lead acid as a method of storing and delivering electricity. However, it was the first battery which was rechargeable. This meant it could be used many times and brought back to its full state of charge when required. It was this that set it apart from other battery chemistries of its time.
Going back to when the first electrochemical cell was invented is a little controversial. There is an ancient Babylonian find which some claim is a working electrochemical cell. Fig. 2 is a picture of what has become known as the “Baghdad Battery”. There is no consensus that these vessels were used as batteries nor had any electrochemical purpose. However, if filled with an electrolyte such as acetic acid, they will produce a current and a voltage. Two dissimilar metals in an ionic conductor – how could they not?
Whatever the real case is, we need to fast forward nearly 3,000 years to the 18th century when two Dutchmen, Musschenbroek and Cunaeus, along with German scientist Ewald Georg von Kleist, made a working version of the Leydon jar. This was essentially a capacitor and still not a true battery. It was the Frenchman Allesandro Volta who invented what we would call the first electrochemical cell in 1800, now known as Volta’s Voltaic Pile, This was essentially a vertical tower of alternating copper and zinc discs with brine soaked cloth between them, Fig. 3
The practical problems with this first battery are pretty obvious (side shorts from leaking electrolyte, keeping the cloth moist etc.). However, it did produce a substantial shock, and when series connections between individual cells were made, it gave an even bigger jolt. Still, it was not an ideal way to store and deliver electricity. Some improvements were made to the design which allowed batteries to made by connecting cells contained in individual glass jars and it was a Scot – William Cruickshank, who made a box construction and laid the plates on their side instead of in a stack. This became known as the trough battery and was, in fact, the precursor of almost all modern battery constructions.
However, the big problem with either of these designs, was that they were not rechargeable. One discharge and you had to put in new plates and electrolyte and start again. Not really a practical solution to storing and providing electricity.
It was not until 1859 that a Frenchman, Gustav Planté, invented the world’s first rechargeable electrochemical cell. This was a spirally wound double sheet of lead separated by a rubber strip, immersed in a sulphuric acid electrolyte and contained in a glass jar Fig. 4.
The plates were electrically charged to lead and lead dioxide with take-off wires attached to each lead sheet. The potential difference between the plates was 2 volts. It gave a higher sustained voltage and current than the voltaic pile but, more importantly, it could be recharged from an electric source without replacing any of the components. This ability to recharge and the higher voltage and longer current durations of this chemistry came at an opportune time in industrialisation and helped in the spread of telecommunications and back-up power where mains supplies were unreliable.
Whilst the battery became an overnight sensation in the energy supply business, it still was limited in its capacity. This remained a problem until a major breakthrough in the commercialisation of the lead acid battery was made in 1880 by Camille Alphonse Fauré. In order to increase the duration of the current during its discharge, he had the idea of coating the lead sheets with a paste of lead oxides, sulphuric acid and water. He then developed the process of curing whereby the coated plates were put into a warm, humid atmosphere.
Under these conditions, the paste mixture formed basic lead sulphates which also reacted with the lead electrodes to form a low resistance bond. The plates were then charged in sulphuric acid and the cured paste was converted into electrochemically active material. This gave a much higher capacity than the original Planté cell.
Also in 1881, Ernest Volkmar replaced the lead sheet conductor by using a lead grid. This grid design had the dual benefit of providing more space for the active material, which gave a higher capacity battery and also enabled better bonding of the active material to the grid.
These two benefits give a lower resistance and a more robust battery with a higher specific energy density. Scudamore Sellon improved on this by adding antimony to the lead to make the grid stiff enough to process mechanically and really start to introduce faster production speeds. 1881 was, in fact, a year of product innovation driven by the newly emerging uses for a portable electric supply, like the first electric vehicle driven by rechargeable batteries, a 3-wheel scooter of Gustave Trouvé which reached a staggering 12km/hour.
An insurance nightmare! In 1886 the first submarine powered by lead acid battery was launched in France. We also had the first tubular design of plate for lead acid battery, designed by S.C. Currie which gave a better cycle life and energy density.
By now lead acid batteries were on a roll and in 1899 Camille Jenatzy reached 109 km/h in an electric car powered by lead acid batteries. With this march of electric power, which includes the installation of the Parisian electricity distribution system in 1882 and the emergence of the Morse electric telegraph in the USA, it was apparent that the lead acid battery had to be produced in a proper commercial fashion.
Start of the modernization of lead acid battery construction
The existing design and lead oxide production process did not lend themselves easily to mass production methods. The demand for lead acid batteries in this age was fast outstripping production capability. New production-friendly methods and battery designs were urgently required. The first breakthrough arrived in 1898 when George Barton patented a new and much faster method of producing the lead oxide used to make the active material invented by Fauré. Barton used the traditional method of melting and oxidising lead using heated air. His innovation was to produce fine droplets created by the stirring of molten lead which was then subjected to a fast-flowing humidified air stream.
- This had the dual advantages of greatly speeding up the process and providing a much finer particle size than the traditional method which required further grinding to give a product suitable for battery active material. It was not until 30 years later that an alternative process was invented by Genzo Shimadzu of the Shimadzu Corporation.
His method was to cast small nuggets of lead and pile them into a rotating ball mill with hot air blown through. This created surface oxide on the nuggets which was brittle and flaked off then was ground down to a fine powder. The air-flow speed was controlled to carry particular sizes of particle out of the mill and store them in silos ready for paste mixing.
These early methods of making lead oxide for the battery industry have remained unopposed for almost a century. Recent developments in finding more environmentally friendly battery recycling methods (lead precipitation from lead acetate solutions) may, in the future, provide alternative production methods, but for now, there is still no practical alternative.
The design of Gaston Planté was not a practical solution for a mass-produced battery. Even the improvements of Fauré and the Scotsman William Cruickshank, who put Planté plate elements in box compartments to form a series-connected battery, did not provide reliability or mass production capability.
It is the Luxembourg engineer and inventor Henri Owen Tudor who is credited with developing the first practical design of lead acid batteries in 1866. He established his first manufacturing plant in Rosport, Luxembourg and went on with other investors to set up factories around Europe. Key to his success was a more robust battery plate, which was longer-lasting than the existing design.
lead acid battery working
Around this time, Genzo Shimadzu was setting up the first lead acid battery manufacturing factory in Japan, and produced a pasted plate lead acid storage battery with a 10 Ah capacity. This was the beginning of the now-familiar Japanese company, GS batteries. Both companies pioneered the modern processes and gave the lead acid batteries greater reliability and life.
The 20th century provided many upgrades for the lead acid battery. The upgrades started with the materials of construction. Up to the first couple of decades in the 20th century, battery cell containers consisted of wooden boxes lined with rubber or pitch. By the early 1920s hard rubber (ebonite) moulding techniques had improved to the point where it was possible to provide multi-celled, leak-proof, hard rubber boxes for housing series-connected lead acid cells. The use of pitch sealed lids made it possible to have sealed, over the top lead connections between the cells. This construction, combined with wooden separators and very thick plates, lasted until the early 1950s.
Lead acid battery life
Developments on the inside of the battery did not entirely stand still during this period. Cellulose fibre separators, impregnated with resin became a lightweight and lower resistance option to the wooden separator. These advantages and its lower acid displacement gave more design possibilities which allowed higher capacities and better high-rate discharge performance. Improvements to the lead-antimony alloys gave a more robust grid, able to withstand more automated processes and eventually allow machine pasting. Additives in the paste like carbon for the negative plate and cellulosic fibres in the positive plate active material, gave a major boost to the cycle life of lead acid batteries.
It was, however, in the early 1950s, when plastics began to become an integral part of our modern way of life, that battery materials and processing methods really began to change. The physical and chemical properties, plus the range of different plastics available, meant that battery construction and productions methods could be seriously overhauled in the second half of the 20th century. Add to this the advances in metallurgy of the lead alloys used in grid making, and the battery industry experienced a serious acceleration in improving performance and cost of its products during this period.
It is really difficult to know where to begin to list the most important developments, so perhaps a chronological order would be the most appropriate. A lot of this is personal recollection rather than direct historical fact, but it is accurate enough to be a reasonable account of the technological steps which led to the present lead acid battery designs. I think going back to the 1960s we saw machine pasting of plates and semi-automatic casting of grids reach higher standards of accuracy and control.
This led to a gradual replacement of hand casting and hand pasting by the much faster book-mould grid casting and trowel – rolling belt pasting methods for single or double plates. Both of these techniques gave higher production levels and better control over the grid and active material weights and dimensions. The initial impact of this was to save money both in labour and material costs. The secondary effect was that it paved the way for the narrower tolerance bands required by recombination batteries.
This was only possible, of course, because of the through-the-wall connection of the battery straps within the cells. This squeeze welding technique is an unsung hero of the battery engineering world. In essence, it is a very clever device using the resistance value of the melted electro-melted lead intercell take-offs to determine when the intercell partition hole had been filled with lead.
This method removed the heavy and expensive top-end lead and enabled a far simpler heated mirror platen to be used for sealing the box and lid. This is without turning the assembly upside down as with the resin and glue methods. Not only did this assembly method improve production rates and reduce costs, but it also virtually eliminated a major cause of warranty returns: acid leakage.
Advances in separator technology also aided the engineering of better production methods as well as addressing a common mode of battery failure, that of internal short circuits. Initially, the mechanical stiffness of the cellulosic and then the sintered pvc separators allowed automatic stacking of battery packs. This led to the development of the cast-on-strap and automatic assembly of lead acid battery. This was a major advancement. The plate joining method up to this point had always been hand burning, using a split bus bar mould with slots into which the plates were inserted by hand. They were then manually welded together by melting a lead alloy stick into the mould using an oxy-acetylene torch.
This is still in use today but confined mostly to larger industrial batteries which are difficult to handle with automated equipment. Apart from low productivity, it has been a major source of warranty failure in the industry. Because the plates are welded upright, there is the possibility that molten lead can leak from gaps in the bus bar mould down between the plates to create an immediate or future short circuit.
Lead acid battery diagram
The method of cast-on-strap, particularly for smaller SLI batteries, has all but replaced the manual hand burning operation. Although an expensive option, it does give zero lead runs, and if the correct lug cleaning and flux is used, also gives a better, lower resistance lug to strap weld. A further refinement to this process is the wrap stacking method. The advent of the polyethylene separator which is highly flexible and weldable has meant that batteries can be made with completely isolated plates.
In this method, either positive or negative plates can be automatically inserted into a separator strip, the strip folded and cut around the plate and then either using heat, ultrasonics or crimping, form a complete seal around the plate. This method, combined with cast-on-strap and automatic group insertion into the battery box, provides high production rates, low warranties and perhaps most importantly, greatly reduces operator lead exposure.
Up to the 1970s, lead acid batteries had some serious flaws. These were high maintenance costs due to water loss with the production of acid fumes and explosive gases on charge. This was a serious cost for many industrial activities, particularly the fork lift truck industry which requires special charging rooms with extract and constant water topping up procedures to prevent battery dry-out. The solution to these problems started to emerge in the 1970s when battery manufacturers switched to low antimony alloys for car batteries.
Lead acid battery types
Although this was initially to save costs, it was soon discovered that combined with voltage-controlled alternator charging in an automobile, water loss from the battery, and therefore topping up maintenance was drastically reduced. Before long, lead-antimony alloys were reduced to 1.8% Sb compared with the 11% used for the first half of the century. This, in essence, gave flooded, maintenance-free SLI batteries.
The idea of using a low gassing lead alloy took up momentum in the 80s when the starved electrolyte lead acid battery started to appear in the now-familiar battery container using the same plates and grid designs as the standard flooded range. This was a completely sealed battery which would not lose water or release explosive gases. Hydrogen and oxygen produced at the electrodes would be held in the battery in an immobilised electrolyte and be recombined to form water.
The acid was immobilised either by mixing with silica to form a GEL or held in suspension in a highly compressed glass mat separator. Although the valve-regulated lead acid battery had been in commercial use since the 1960s (Sonnenschein then Gates), these designs used pure lead for the grids, which is very soft. This meant that the design possibilities and processing methods were limited.
New alloys were designed which completely removed antimony and substituted calcium as a hardening agent. This effectively raised the hydrogen and oxygen overpotential on lead above the 2.4 volts per cell charging threshold, which would allow recharging within 15 hours, or one cycle per day operation. However, serious problems occurred in the early 1980s when massive battery failures due to what is termed premature capacity loss or PCL hit most battery companies very hard. This was effectively a very rapid capacity loss suffered by lead acid batteries within the first few weeks or months of being in service.
It was eventually solved in the 1990s with the introduction of tin into the lead alloy. The precise action of tin on the interface and the integrity of the active material is debatable, but it was found to work. One side effect was that if the balance between tin and calcium in the positive grid was wrong, then this could lead to catastrophic corrosion failure of the grid. The Work of David Prengaman in the 90s resolved this and we now enjoy reasonably problem-free and maintenance-free lead acid batteries.
Lead acid battery manufacturing machinery
During the 1980s the tubular design of plate also underwent some radical changes. From its beginnings in 1910 until the mid-60s it had used individual porous rubber cylinders mounted on the spines of the grid to hold the active material. This was superseded by the use of individual resin-impregnated fibreglass (pg) tubes. Because of the high scrap rates and physical difficulty of dealing with this product in a mass production environment, the woven multitube gauntlet was developed. This created a single unit of the unfilled grid and active material carrier.
By the 1980s the Multi-tube PT Bags had almost completely taken over from the pg tube which was only still in use due to the false economy of having a lower cost. The PT Bags gauntlet now allowed automation of the casting and spine insertion segment of plate production. Later developments in the late 80s extended this to filling the plate with active material.
It was Hadi who led the way to produce a completely automated line from spine casting through to filling, capping and drying/curing of the plates. It was during this period that automated, either wet or slurry filled methods were also introduced. These methods were far better from a health and safety standpoint as they reduced the lead in air problems of dry powder fill alternatives.
The second millennium had been concentrating on new issues for the lead acid batteries. The stop-start, and some other applications, have highlighted problems for flooded lead acid batteries which operate in a partial state of charge (PSoC) conditions. In this, the active material in the plates becomes coarser with a lower effective surface area. The material is, therefore, less reactive, giving lower capacities and lower high rate discharge capability.
To combat this substantial work is ongoing to find additives, namely carbon in different forms which prevent this coarsening and improve the conductivity of the active material. This also improves charge acceptance (important in start-stop use) as well as providing nuclei for precipitation in PSoC conditions to prevent AM particle coarsening. Some success has been reported, but there is no substantive evidence that these expensive additives have been universally adopted.
Substantial work has been done by suppliers of additives and separator manufacturers to improve both the PSoC and electrical performance of lead acid batteries. New separator designs which prevent stratification of acid in PSoC conditions are being marketed, as are separators with built-in additives to help reduce particle coarsening in the active material. This is becoming increasingly important as the traditional SLI market changes to accommodate the rise of the electric vehicle and its hybrid variants.
Lead acid battery applications
As the internal combustion engine begins to fade from our roads and the EV market continues to expand, the lead acid battery, although still the highest-selling technology in today’s energy storage markets, will have to undergo further adaptations. New designs, such as the bipolar version offer much higher power and energy densities and lower cost due to using substantially less lead in their construction.
The rise of new markets, particularly energy storage, offers fresh opportunities for lead acid batteries. Concentrating on better cycle life, energy efficiency and lower cost will give a far more attractive ROI to those businesses installing grid-scale systems. Despite the possible decline in the SLI market from the growing EV sector, lead acid batteries still have huge market potential. However, it depends as much on marketing as it does on technology. New battery systems, particularly Lithium ion battery chemistries, still have the significant environmental concerns of lack of recycling or disposal infrastructure on top of their high initial cost.
This could mean an expensive end of life shock if battery disposal costs are applied, which for many companies with large battery investments could be substantial. This and the high cost of purchase mean that the ROI for lithium ion battery is far less attractive than lead acid battery in most existing and emerging applications. In the EV market, for example, many electric rickshaw owners do not want the capital cost of a lithium ion battery and are happy to use its flooded lead acid counterpart.
In summary, what we can say is that lead acid is still evolving to meet the new applications and new market environments. With new, cheaper and more environmentally safe methods of recycling lead acid batteries being developed, it is still the most environmentally friendly, reliable and safe battery that you can buy. And it comes at a very low price. Think of that the next time that you make a comparison between competing battery chemistries.