By - Prof. Homendra Naorem
Department of Chemistry, Manipur University
In a state like Manipur where
issues continue to eclipse every other issues (and justifiably so sometimes), important events like the announcement of the Nobel Prizes understandably fails to hit the headline of any local dailies or topic of discussion or create any ripple in the state,save the minority scientific community in the state. With clock-like regularity, the Royal Swedish Academy of Sciences has announced that the Nobel Prize in Chemistry for the year 2019 would be given to three Chemists:(i) John B. Goodenough, 97, Professor at the University of Texas; (ii) M. Stanley Whittingham, 77, Chemistry Professor at the State University of New York at Binghamton, and (iii) Akira Yoshino, 71, of Asahi Kasei Corporation and Chemistry Professor at Meijo University, Japan for ‘their work leading to the development of lithium-ion batteries, which have reshaped energy storage and transformed cars, mobile phones and many other devices — and reduced reliance on fossil fuels that contribute to global warming’.Humankind has hugely benefitted and continues to benefit from their scientific researches. It is without any doubt a befitting tribute to the memory of Alfred Nobel, the Chemist, who instituted the Prize by donating his life time earnings to ensure the fruit of scientific research benefits the humankind. The prize carries an amount of 9 million Swedish krona (about ¹ 7 crore), to be shared equally among the Laureates. What is a battery or to be precise lithium-ion battery?
The term battery now is so common and popular that it hardly needs any explanation. But when it comes to who first coined the term, one needs to google! The word ‘battery’ of course means a series of objects grouped together to perform a function, like a battery of artillery or a battery of tests, etc. It was Benjamin Franklin who first used the term ‘battery’ in 1749to describe a series of capacitors linked together for his ‘electricity experiments’. Later, the term was used to denote electrochemical cells linked together for the purpose of providing electric power by Italian Physicist, Luigi Galvani (associated with Galvanic cell) using mostly copper and zinc rods (electrodes) immersed in acidic solution (electrolyte). While trying to produce energy from chemical reactions, Alessandro Volta created the first batteryin 1800known as the ‘Voltaic pile’, which can produce stable supply of electric current. Despite its two major problems - the leakage of the liquid electrolyte and short life span (about an hour) - the voltaic battery in different forms was in use for more than hundred years! The leakage problem was circumvented by laying the voltaic pile on its side to form it as ‘trough battery’ by William Cruickshank of Scotland. In 1835, William Sturgeon demonstrated that the short life span of the voltaic pile caused by the degradation of the zinc due to impurities and a build-up of hydrogen bubbles on the copper could be increased by treating zinc with mercury which preventedthe rapid degradation of zinc.A breakthrough in battery came in 1836 when the British Chemist John F Daniell invented the so-called ‘Daniel cell’ using a second electrolyte that reacted with the hydrogen, preventing its build-up on the copper cathode – copper dipped in copper sulphate solution and zinc dipped in zinc sulphate solution which were interconnected through a porous membrane (or salt bridge). Its impact was so much that Daniell’s two-electrolyte battery was instrumental in the functioning of the then budding telegraph networks in Britain and elsewhere.Most of the batteries until 1800 were in a ‘liquid state’and suffered from poor maneuverity.A real breakthrough in battery came in 1866 when Georges Leclanché created a battery using azinc anode, a manganese dioxide cathode, and an ammonium chloride solution as the electrolyte, which eventually led to the development of the dry cell with the introduction of an electrolyte paste out of ammonium chloride and plaster of paris byCarl Gassner. Hepatented the new ‘dry cell’ battery in 1886 in Germany. In the 1950s, the Union Carbide company introduced ‘Eveready’dry cells by replacing the ammonium chloride electrolyte with an alkaline substance, based on the chemical formulation of Jungner in 1899. Alkaline dry cell batteries could hold more energy than zinc carbon batteries of the same size and had a longer shelf life.Alkaline batteries rose in popularity in the 1960sovertakingthe zinc-carbon batteries, and become the standard cell. Since the chemical reactions in such cells are not reversible, the battery will not be able to produce current once the reactions come to completion or equilibrium causing the battery to be dead. Such batteries are known as primary batteries. Can one develop a battery based on a reversible chemical reaction avoid the unwanted dead of the battery? The thought has given rise to the birth of secondary or rechargeable battery. But before that, let us try to understand the working principle of a battery from scientific perspectives.
In the realm of electrochemistry, there are broadly two types of cells: (i) Electrolytic Cell in which an electric current causes a chemical reaction to take place and (ii) Electrochemical (Galvanic)Cell in which electric current is produced as a result of a chemical reaction. A cell has necessarily three components, apositive electrode, a negative electrode (known as anode and cathode respectively)and some kind of electrolyte that separates and chemically reacts with the electrodes and also allows the flow of electrical charges between the electrodes.A battery is a combination of one or more such cells (joined in series, parallel or both) whose chemical reactions create a flow of electrons (electric current) in a circuit.However, in a commercial battery, the electrodes are generally indicated in the form of terminals, a + terminal (sign on the battery) indicates the cathode while the anode is indicated by a –terminal; anodes and cathodes should not confused with + or – veterminals of the battery.When the terminals of a battery are connected to an external circuit, oxidation (loss of electron) occurs at the anode generating cations (positively charged species) and electrons. The electrons flow through the circuit and the cations through the electrolyte to the cathodewhere reduction (gain of electrons) takes place. When the material in the anode or cathode is consumed or no more chemical reaction occurs, the battery will no longer produce any current and hence is said to be dead. That is exactly what happens in a primary battery. On the other hand, in secondary cells or batteries,the chemical reaction may be reversed by passage of an external current making them ‘rechargeable batteries’. In otherwords, a rechargeable battery functions not only as electrochemical cells while discharging but also as electrolytic cells while recharging.
Perhaps the first rechargeable battery was created by the French Physicist Gaston Planté in 1859 using two rolled sheets of lead submerged in sulfuric acid. The advantage of such batteries is that the chemical reactions in the battery may be reversed when an external current is passed through it.Another major improvement came in 1881 when Camille Alphonse Faure introduced lead plates instead of sheets laying the foundation for the modern day lead acid battery which are still widely used in automobiles and other industries.It however employs a liquid electrolyte limiting its portability and user-friendliness. Such batteries are not suitable for small hand held electronic devices like radio, mobile, or communication satellites, etc. A portable form of rechargeable battery based on nickel oxide hydroxide and metallic cadmium as electrodes, known as ‘Ni–Cd’ battery, was created by Jungner of Sweden in 1899 which was widely used in portable power tools, electronic devices, etc.In another major breakthrough,COMSAT (Communications Satellite Corporation) developed the nickel-hydrogen battery for use in communication satellites in 1970s with the storageof hydrogen in a pressurized, gaseous form. In around 1989, several companies launched the nickel-metal hydride (NiMH) batteryin the consumer market providing a smaller, cheaper alternative to the rechargeable nickel-hydrogen cells.The rechargeable batteries like Ni-Cd, Ni-H, NiMH, ruled the market until the entry of the Lithium-ion battery in 1991 that revolutionized the world of battery!Why lithium? Are the metals chosen arbitrarily? Metals are chosen not arbitrarily but on the basis of their tendency to loseelectrons (oxidation) as indicated by the so called standard oxidationpotential (SOP). Lithium the lightest metal has the highest SOPof about 3.05 Volt, for zinc and Ni it is 0.76 and 0.25V respectively while copper has -0.35V. It basically means that if zinc and copper were to be left in open air zinc will get corroded(oxidize to Zn+2 ions) faster while copper would remain almost unaffected. Because of the high oxidation potential, lithium has always be the preferred metal but for its reactive and explosive nature when in contact with air or water.
The pace with which the invention of Lithium-ion battery gained owesperhapsto the oil crisis during mid 60s and 70s when chemists like Whittingham working on the development of fossil fuel free energy sources. He tried to develop battery using lithium metal as anodic material instead of nickel or other metals. How about the cathode? Then came the most innovative creation from Whittingham who developed acathode for the lithium battery using titanium disulphide which can intercalate lithium ions in it.Only chemist can tailor-make such materials infused with desired properties! He then developed a battery with just over 2 Volts using a lithium based liquid electrolyte but it has huge potential for future developments. In such battery, lithium ions produced at the anode moves through the electrolyte to the cathode while the electrons from the anode flow through the external circuit and eventually to the cathode while discharging. But because lithium is highly reactive, such battery always ran high risk of getting exploded unless handle carefully. Around this time, another chemist, Goodenough not only predicted but synthesized a metal oxide that can intercalate lithium ions to demonstrate that a metal oxide and not sulfide is a better candidate forthe cathode. In 1980, Goodenough reported that when cobalt oxide intercalated lithium ions is used, it can produce as much as 4 volts. Following the results of Whittingham and Goodenough, Akira Yoshino for the first time in 1985 built the commercially viable lithium-ion batteryusing a carbon material (known as petroleum coke)intercalated with lithium thereby making it much less prone to explosion that was there with metallic lithium. Eventually, Sony marketed the first commercial lithium-ion battery in 1991. Unlike other rechargeable batteries, lithium ion battery is not based on a reversible chemical reaction that eventually consumed the electrodes buton the flow of lithium ions from the anode to the cathode through an electrolyte while discharging and from the cathode to the anode on recharging. In order to minimize the risk of getting the electrodes short-circuited in case the electrolytes get evaporated due to the heat generated in the process, a micro-porous polymeric insulator permeable to lithium ions in the form of ‘separator’ coated with the electrolyte is employed. This greatly reduces the possibility of the battery getting exploded while recharging. At present, a typical lithium-ion battery uses lithium intercalated graphite (LiC6) and lithium intercalated metal oxide (LiCoO2)as the electrodes and an alkyl carbonate LiPF6 (for example) as the electrolyte. Most of the materials employed in the present day lithium ion battery are patented and hence their exact chemical compositions are not known.The fact that no alternative to lithium ion battery has ever been claimed in the last more than 30 years should vouch the importance of the lithium ion battery. It may be still in use in the next few decades perhaps with more added attributes! However, there are still researches towards bettering its discharge-recharge cycles from the present about 3000 to about 10,000 cycles (about 20 years – one battery for life time!) and to increase its single cell voltage from about 3-4 Volts by five folds, current density, etc. One of the tricks in achieving the goals among othersis replacing the lithium ion storage medium from graphite to silicon or silicon based materials which can effectively but reversibly intercalate the lithium ions.
With the announcement of this Year’s Prize, Prof John B. Goodenoughat 97 years stands out as the oldest person to receive a Nobel Prize in any discipline! Even at this age, he still goes to his research lab every day. More than the Nobel Prize, he is more concerned, as he revealed, with the completion of the doctoral program (PhD) of his final student working on batteries! He further commented, ‘I don’t know when I’ll be taken. But I suppose it’ll be one of these days soon. At my age I don’t take someone on who is going to do a four-year PhD stint. My last student is a pretty good boy. I plan to see him graduate. That’s my plan. But of course I’m not in control. I live day by day, that’s all I can do’. Compare it with the working environment in most of the Indian (including Manipur) Universities where any scientistafter 65, is treated more like a trespasser than a possible source of innovative ideas,thoughts, expertise, let alone guiding a research scholar - the scientist is asked to abandon his research well before 3 years prior to his attaining the magic 65 years. Will the award of this year’s Nobel Prize to a nonagenarian who still is actively engaged in research cut any ice with the younger generation in pursuit of knowledge and wisdom!