Background to batteries
The beginning - the history of the electro-chemical energy reservoir started with the scientific study of electricity.
Luigi Galvani (1737-1798), who first discovered electrical phenomena, and Alessandro Cont di Volta (1745-1827), who developed the first voltage generator, are two names that are central to the story, and which live on through terms such as the “galvanic cell” and “volt”. In experiments conducted in 1789, Luigi Galvani noticed that a frog’s leg began to twitch when it came into contact with two different metals. From this, he deduced a correlation between electricity and particular muscular functions.
Galvani's frog experiment
Alessandro Cont di Volta
Ten years later, in the year 1799, A.C. di Volta built the first basic battery: he assembled alternating layers of copper and zinc, stacked on top of one another, and between each layer he inserted a piece of cardboard soaked in a salt solution. When the layers were conneted by wires, this “Voltaic Pile” created energy. And when several of the piles were connected in a row, the voltage increased.
In 1802, Johann Wilhelm Ritter, who was a scientific collaborator of Goethe’s, created a battery called the “Ritter pile”. The stack consisted of copper and cardboard layers soaked in a table salt (sodium chloride) solution. This apparatus could be charged with an electric current and produced electricity when discharged. The “Ritter Pile” is the forerunner of the modern battery.
Johann Wilhelm Ritter
Around 1840 to 1850, two men named Sinsteden and Planté began employing the first lead batteries (made of lead, sulphuric acid and lead dioxide), which were used to store energy for telegraph-related experiments. Both were using lead plates as electrodes that had been built up to a certain capacity through repeated charging and discharge. However, these batteries were not yet suitable for mass production.
Thanks to industrialisation, electrochemical energy storage began to develop quickly. Dynamos and bulbs were discovered towards the end of the 19th Century, and the demand for storing energy grew quickly. Around 1880, once Fauré had filed a patent for producing paste-covered plates for lead batteries, they started being manufactured on an industrial scale. Continuing in the same vein, two men called Jungner and Edison created the nickel-cadmium battery. It wasn’t long before it could be mass-produced.
The lead battery’s early years
The physicist Fauré covered both sides of a lead mat with a paste made from lead powder and sulphuric acid. This enabled him to achieve a particularly high capacity after the first charge (the “formation”), which paved the way for the industrial production of the battery. In the wake of this, a number of companies were established. One of them was La Force et La Lumière S.A., where W. Thomson worked (who would later be known as Lord Kelvin of Largs, the man who gave his name to the absolute temperature scale). To begin with, the idea was to build giant energy stores, with W. Thomson conceiving a plan to supply electricity from the Niagara Falls to the town of Buffalo. With 80,000 volts (V) being generated and supplied to Buffalo via a 40,000 cell battery, households in the town would then be supplied with 100V of network power with a tap of 50 cells each. Due to various reasons, however, the plan never came into fruition.
With their spiral-wound positive and negative electrodes, Fauré cells were not very durable and failed after only a few charge and discharge cycles - this was a major obstacle when it came to producing batteries on an industrial scale.
A major advance was made in 1881 - J. Scudamore Sellons had the idea not to apply the paste to a flat plate, but to work it into a perforated plate instead, creating better adhesion. He was the first metal scientist to use antimony alloy as a lattice material - something that would prove so important later. It’s not known to what extent each man knew about the other, but the same year, Ernest Volckmar developed a lead grid known as a "pasted grid" that soon became commercially available in many different versions.
That same year, Charles F. Brush registered a patent for a lead electrode with a large surface area and corrugated surface. Both these plate types (pasted lattice plate and large-surface plate) are still much in use today. Even the tubular plates now commonly used in Europe and Japan for traction and stationary batteries have a long history – S. C. Currie invented the basic form in 1881.
In the case of tubular plates, a lead rod about 8mm in diameter lies at the centre of the tubule – something that is still a key feature today. An outside layer of woven or unwoven material gives the active material mechanical assistance.
The special role of alloys in a lead battery
Because corrosion spreads gradually through the metal and turns lattice material into lead dioxide, this system is unstable, causing the grid to lose its mechanical strength and its conductivity. But a protective layer slows the corrosion to such an extent that if the battery components are well positioned, the battery’s operating time is not compromised.
The potential of the negative electrode lies at 0.35V below the equilibrium potential of the hydrogen electrode. Under normal circumstances, hydrogen should be released from the weak sulphuric acid solution, discharging the battery. However, using lead significantly reduces the build-up of hydrogen, and the gas is produced very slowly. Thus “self-discharge” at the negative electrode cannot be stopped entirely, but it happens so slowly that it can be tolerated.
Pure-lead (refined lead) lattice alloys were derived from the large-surface plate dating back to Planté, with a small layer of active material being formed on a large cast via a process of electro-chemical oxidation. Unalloyed lead is an unsuitable material for a light lattice because it is not solid enough for further work. Furthermore, pure-lead lattices or plates are almost impossible to manage in a standard assembly process.
In the USA, because of its geography and many relay stations spread over large distances, this posed a big problem - which was why BELL Laboratories was urgently looking for a way to overcome it. From 1935 onwards, research was carried out exploring the possibility of using lead-calcium alloys instead of lead-antimony alloys. Eventually, these were implemented in BELL’s fixed battery installations. Despite extensive pre-testing and field tests, they proved highly disappointing, with the operating life of the batteries frequently way below initial expectations.
To cope with growing lattice-sizes, BELL Laboratories created stationary batteries with saucer-like electrodes made from pure lead. In 1970, these were rolled out at BELL’s telephone installations.
The addition of metals contributing to the fine structure of the solidified material (fine-grained alloying) would prove important. Otherwise, alloys that contain small amounts of antimony can’t always be poured smoothly. Here, the addition of small quantities of selenium (200g/ton) proved to be particularly effective; the selenium forms fine lead-selenide particles (PbSe) that act as foci during the solidification process, enabling crystal formation and allowing the desired finely grained structure to emerge.
Lead batteries made with these alloys have such low water loss that, for “stand-by” applications and under normal conditions, they will only need a refill after more than 5 years have passed. The remaining antimony content stabilises the cycle sequence to such an extent that they can reach more than 1,000 charge/discharge cycles. Under normal operating conditions, standard batteries such as these – carrying the “maintenance free” DIN classification – need no extra water throughout their standard 5-year working life.
Further development of the lead battery
At the end of the 19th century the lead battery as we know it was already being manufactured including the three electrodes that are still the norm today. Development of the battery continued over the hundred years that followed, and better knowledge about determining factors permitted better production processes and new plastics to be used as material for separators and containers. We will only outline a few of these developments here.
Tubule electrodes work efficiently with the active material and offer a high level of cycle stability. In the early days, the tubules were made from slitted hard rubber, but after the second World War, braided glass fibres – a woven material made from glass fibre and other synthetic fibres, or a web or felt made from a pure plastic (polyester) - were introduced as a new material.
The valve-regulated lead-acid battery (VRLA)
Valve-regulated lead-acid batteries significantly reduce the need for maintenance. They work according to the same principle of the air-tight nickel-cadmium battery. The oxygen produced at the positive electrode does not leave the cell - instead, it is reduced back to oxygen ions (O2-) at the negative electrode and combined with hydrogen ions (H+) to form water. Thus, oxygen produced by overcharging the positive electrode is balanced by oxygen reduction at the negative electrode. If the internal oxygen cycle is running perfectly, there is no loss of water.
Since a certain amount of hydrogen build-up in lead batteries is inevitable, it is impossible to achieve perfect internal oxygen circulation – even at a cell’s electrically-neutral equilibrium potential. Another problem is the inevitable lattice corrosion at the positive electrode. Both of these secondary reactions limit how efficiently oxygen can circulate internally, making a certain amount water loss inevitable. For sealed lead batteries, this constitutes their principle point of difference with nickel-cadmium batteries.
To achieve an effective internal charging/discharge cycle, oxygen must reach the negative electrode as a gas. However, in a liquid electrolyte, the process would be too slow - thus, it is achieved either by adding silicon dioxide (SiO2) gel - shrinking it and forming gaps through which the gas can pass - or the acid is absorbed by a glass mat of extremely fine glass fibres (with a micrometer(µm)-thin diameter). In these absorbent glass mats, gas can pass through large pores left unfilled by the electrolyte.
Attempts to make static electrolytes out of gel had begun even before the end of the 19th century. Like “dry batteries”, the idea was to prevent any spillage of sulphuric acid even if the container was breached. At the time, nobody had given much thought to applying this method to lead batteries, but in 1950 a battery company called “Sonnenschein” revived the idea. Though at first the ambition was to make smaller tilt-proof batteries (which were equipped with valves and therefore shared some of the characteristics of valve-regulated lead-acid batteries).
In the seventies, a glass fibre mat with a µm-thin diameter began to be used, allowing valve-operated lead-acid batteries to be used more widely. Originally designed as a micro-filter, the ability of the material to absorb the sulphuric acid electrolyte meant that it could be used as a separator, preventing short cycles (short circuiting) between the electrodes and simultaneously holding the electrolyte in place. Another advantage of the technology was that the batteries could be assembled at conventional plants. Moreover, they have such low internal resistance that the batteries could supply high discharge currents very effectively. At the end of the seventies, valve-regulated starter batteries began to be used for cars. But for various reasons they were not a success, and the battery’s advantages as a starter were overlooked.
However, the battery proved very successful for telephone installations, and a trend was started of using sealed lead batteries for many stationary applications (for example, today most uninterrupted power supply installations are equipped with valve-regulated lead-acid batteries.) This success was due not just to their low maintenance requirements and low quantities of hydrogen production, but also because they could safely be placed next to other electronic components without the danger of corrosive vapours leaking out of them.
Valve-regulated lead batteries continued to be developed with a jellied electrolyte (gel), and in the seventies the same principle was applied to larger batteries. Today, there are gel electrolyte batteries with a capacity of up to 3,000 ampere hours (Ah) per cell, with various different models for stationary and/or mobile applications. VRLA batteries have also been a step forward in environmental terms, because the electrolyte is kept locked in a glass mat, or in a silicate gel.
Besides the specific developments above, there have been several significant more general lead-battery innovations over the decades.
First, spacers made of hard rubber or thin blocks of wood were used to separate the electrodes. In 1915, a porous separator made from hard rubber was patented. In 1924, a similar one was invented in Germany with latex as the base material. In both cases, the objective was to create a precise system of pores using elastic material and filler - and, with a few modifications, these are still in use today. After 1945, plastic was the main material used for separators – especially PVC and polyethylene. Likewise, battery containers were increasingly being made from plastics, instead of glass or hard rubber.
The constant improvement of electronic components have paved the way for better charging technology. Car batteries’ average state of charge could now be increased and battery life extended. Monitoring of stationary batteries has improved, preventing unexpected outages. In the last couple of years this trend has continued, and today you can get devices that continuously monitor the battery.