A Long Journey of Lithium: From the Big Bang to Our Smartphones

Lithium was nucleosynthesized in the first 5 min of The Big Bang around 13.7 billion years ago, together with hydrogen and helium. It is the very first metal in the period table (atomic number 3), the lightest metal (density 0.534 g cm−3), and the metal with the lowest electrochemical potential (−3.04 V vs standard hydrogen electrode). All these characteristics fortuitously combine to make Li the most power anode material for energy storage. October 10, 2019, Stockholm, Sweden. The Nobel Prize Committee announced that the Chemistry Award of that year was given to Goodenough, Whittingham, and Yoshino for their key roles in developing Li-ion battery technology. This long-overdue prize instantaneously electrified the research communities of electrochemistry and battery materials/chemistry. It is not only a long-overdue recognition for these chemists, but also marks a significant milestone to the saga of lithium that has become such an essential part of our daily life, in the hand-held smartphone that everyone walks with, in the increasing number of electric cars running on the roads, and in the grids that deliver electricity to millions of families.1 Lithium element was nucleosynthesized within the first a few minutes of The Big Bang some 13.7 billion years ago (Figure 1).2 It was one of the three primordial elements of our universe, but for some reason still unclear today (so-called “lithium deficiency”), its abundance is far lower not only than the other two primordial elements (hydrogen and helium) but also than most of the heavy elements whose syntheses require much harsh conditions such as star formation or supernovae (Figure 2).3, 4 On our planet, the abundance of lithium is not only rare, its distribution is also extremely uneven. Most of lithium reserve in earth crust deposit in a chain of salt lakes on South American continent, in a narrow area intersected between Chile, Bolivia, and Argentina known as “The Lithium Triangle (Figure 3).”5 In 1817, a young Swedish chemist Arfwedsen found a new alkaline existing in a mineral Pedalite (LiAlSi4O10), which consumes more acid during its neutralization than all known alkalines (potassium hydroxide and sodium hydroxide). His mentor Berzelius named the alkaline “lithion,” apparently from the Greek word (λιθoς, or "stone") to mark its first discovery from a mineral. The corresponding “radical” in the alkaline, Berzelius suggested, should hence be called “lithium.” This word first appeared on paper in a letter written by Berzelius dated January 1818 (Figure 4).6 Almost immediately after lithium’s discovery, people attempted to isolate its pure form, but its extremely high chemical reactivity presents severe challenge to anyone doing so. Arfwedsen and Gmelin tried with chemical means, and both failed,7 while Sir Davy adopted an electrochemical approach, which has been proven successful in isolating both sodium and potassium. When applying a Volta’s pile on heated lithium carbonate in December 1818, he almost succeeded and documented “…bright scintillations on a platinum electrode ….”8 Since we cannot be certain that the scintillations represented pure form of lithium deposited on platinum, nowadays we generally credited Brande for the isolation of pure lithium, who reported in a reproducible manner that a “brilliant white and highly combustible metallic substance was separated” when a Volta’s pile was applied on lithia (lithium oxide).9 Hence, the fate of lithium was associated with electrochemistry ever since its birth. In fact, till today, lithium metal can still only be produced via the electrolysis of molten salts, which is the consequence of its extreme chemical and electrochemical activity. In the hundred years following it discovery, lithium found its major use as a cure for gout, asthma, depression, hangover, and then as panacea for essentially every illness. People started to use it as additives in foods and drinks. One legacy of that era is the lime soda “7Up,” where “7” stands for the atomic weight of lithium (6.95), and “Up” for the mood elevation effect of lithium. This trend of lithium excessive use finally led to fatal overdoses, and eventually its regulation by Food and Drug Administration in USA.10 The only fleeting encounter of lithium with battery in those early days was perhaps a patent filed by Edison in 1908, in which he claimed that adding lithium hydroxide to the electrolyte in his nickel-iron battery led to 10% capacity increase and better storage retention, although he admitted that he did not know (and probably did not care either) why the presence of lithium in the electrolyte brought such benefit.11 A more rigorous study revealing lithium’s power in (electro)chemistry appeared nearly 100 years after its discovery, when Lewis and Keyes accurately measured the potential of lithium metal in reference to a saturated calomel electrode, which is 3.3044 V, and reported that “…this is the highest electrode potential hitherto measured.”12 This statement remains true today, as there has not been, and most likely there will never be, any element in the periodic table that can be more electropositive than lithium. This fact sets the foundation for all modern efforts in quest of a battery based on lithium metal or its derivatives (lithium alloys and intercalation compounds). The serious pursuit of high-energy lithium-based batteries started in 1950s, which were mainly funded by Defense Department and NASA and documented in numerous reports of this period submitted to government. Initial efforts focused on metal fluorides, sulfides or oxides as cathode and lithium as anode.1 In retrospect, those chemistries are full of pitfalls arising from all the selected components, some of which are not resolved even today, such as the dendritic growth of lithium, and the (electro) chemical irreversibility of conversion-reaction chemistries. In these reactions, the reactants have to experience the breaking and reformation of lattice structures in each cycle. Nevertheless, as a side product from these efforts, primary (non-rechargeable) lithium metal batteries were developed and commercialized. Till today these batteries still hold a niche market. The breakthrough concept that resolved the irreversibility issue of rechargeable battery chemistries was a derivative from the so-called “Host-Guest” chemistry, which studies the reversible formation/dissociation of host and guest species through non-covalent bonds. The group of Huggins at Stanford University in 1970s was investigating such compounds of various layered structures, whose interstitial voids or tunnels could accommodate different guests,13 and how guest species move in these structures. Two members of this group, Whittingham and Armand, were to become eminences later in battery field. Realizing that it is possible for solids to conduct ions, these young scientists gathered in 1972 at Belgirate, Italy, and brainstormed on how to apply this new class of materials to solve the battery problems. The combinations of materials yielded diversified exotic battery chemistries, some of which are still under exploration as the possible next-generation batteries, such as sodium/sulfur, lithium/sulfur, and lithium/air. After leaving Stanford, Whittingham joined Exxon Mobile, which, pressurized by the Oil Embargo and the pessimistic outlook for the global oil reserve, was actively seeking alternative energy source. It was here that Whittingham discovered that titanium disulfide (TiS2) could serve as an ideal host for lithium-ion (Li+), which moves at an astonishing speed at room temperature and excellent reversibility (Figure 5a).14 Whittingham immediately correlated such reversibility with the minimal structural change of TiS2 during its accommodation of Li+.15 Thus, a revolution occurred upon replacing the difficult conversion-reaction chemistry with an intercalation mechanism, which brought everlasting effect on the strategies in designing reversible cell chemistries, although certain compromise in energy density has to be accepted because of the extra masses associated with the host structure. A cell constructed on TiS2 and lithium metal displayed such remarkable rechargeability that a model coin cell built in 1976 still worked after nearly 40 years.16 While TiS2 is electrochemically robust, it is unstable when exposed to moist air, which hydrolyzes the sulfide and generate unpleasant and toxic hydrogen disulfide. More importantly, TiS2 sits at a low potential against lithium, thus it could only offer a low voltage (<2.5 V) battery. Inspired by Whittingham’s work, an Oxford professor Goodenough believed that one could obtain a cathode material of both stability against moisture and high voltage against lithium by replacing sulfide with oxide. After screening a series of transition metal oxides, in 1980 Goodenough identified lithium cobalt oxide (LiCoO2) as the winner (Figure 5b). It is a 4-V class cathode and has a layered structure similar to TiS2 that can reversibly accommodate and release Li+, at high speed.17 Later it would be the cathode material in the Li-ion batteries that power billions of smartphones, laptops, and all other portable electronic devices around the world, but at that time, lithium metal was still the only anode material in people’s mind. Around the same time, another event of extremely high importance but much less known to the public also occurred, which was the proposal by Armand in 1980 to construct a cell using intercalation compounds as both anode and cathode materials. He predicted that, due to the minimal structural changes in both electrodes, a cell of superb reversibility should ensue, as long as the potential difference between the two intercalation hosts can produce a meaningful voltage (Figure 6).18 The additional masses of both intercalation masses will of course induce even more compromise in energy output, thus this concept did not stir enthusiasm at a time when the lithium metal anode was still considered possible. What made this concept practically difficult is also the absence of a proper intercalation host that can serve as anode host. Most of the intercalation materials known at the time were based on either chalcogenides (sulfides or selenides) or oxides, all of which reside at relative high potentials versus lithium, hence producing a small voltage (<3 V) when coupled with another intercalation host serving as cathode and suffering from heavy penalties in energy density. These shortcomings can be evidenced by the first experimental “rocking chair” cell constructed by Scrosati et al. following Armand’s concept.19 What it took to change people’s opinion was a major recall triggered by the volatile lithium metal. After Whittingham published his work on TiS2 in 1976, Haering, a professor at University of British Columbia in Canada, found that the naturally occurring molybdenum disulfide (MoS2) has the same basic structure as TiS2 and very similar electrochemical behavior.20 The heavier mass of Mo than Ti does lead to lower energy density, but this disadvantage would be compensated by the fact that British Columbia is sitting on huge reserve of MoS2, while TiS2 has to be synthesized via a costly process. A new company Moli Energy was thus established, and by late-1980s, it was racing with potential Japanese competitors to commercialize the very first lithium metal rechargeable battery. In December 1988, it started shipping the AA-size Li/ MoS2 cells for cell phone and laptop manufacturers in Japan. Within four months, numerous fire accidents occurred in those cells, prompting a total recall by Moli Energy.1 This incident forced people to look for alternatives to lithium metal anode, and Armand’s dual-intercalation concept suddenly became not only attractive but necessary. Even before Moli’s recall, a research team at Asahi Kansei, a Japanese petrochemical giant, had been working on a lithium metal-free battery.21 They adopted Goodenough’s cathode LiCoO2, a polyolefin porous separator soaked with non-aqueous electrolyte, and a carbonaceous anode that serves as the host for Li+. Petroleum coke, an amorphous carbon from the residual of petroleum fractionation, was identified as an ideal host. The first lab cell of such dual-intercalation configuration was demonstrated by Yoshino in 1983,22 and then in June 1986, led by Kuribayashi, a team of engineers from Asahi Kansei successfully assembled this chemistry into commercial cylindrical configurations in a battery company in Boston, Massachusetts. This should be viewed as the official birth of Li-ion battery, although its anode was not graphitic carbon, which majority of modern Li-ion batteries are now based on. The eventual commercialization was realized by Sony, which announced in March 1990 that a new rechargeable battery will be manufactured to power camcorders. Tozawa named it “Li-ion battery” to reflect the fact there was no lithium metal therein.23 Two years later, the engineers in Sanyo figured out how to make graphitic anode work.24 Their key know-how: Using an indispensable molecule called ethylene carbonate as the main electrolyte solvent. Dahn pointed out that it was EC that sacrificially decomposed to form a protective interphase.25 Not many electrolyte solvent can form such interphases, and the relation between the chemical structure of solvents and their interphasial chemistry remains not very well-understood till today (Figure 7).26 In the following decade, Li-ion batteries powered the revolution in portable electronics, as the energy density increased from 80 Wh per kg of the 1st generation Sony Li-ion battery to nearly 300 Wh per kg. Nowadays, we are carrying at least two Li-ion batteries everyday as we leave home.27 In 2000, Li-ion batteries were first adopted as automotive power by a small company in Silicon Valley, AC Propulsion, which built a hand-made sports-car “tzero.” Although not manufactured by scale (only 3 were built), its amazing acceleration and the noiselessness while doing so made deep impression on a couple of entrepreneurs in Silicon Valley, Eberhard, and Tarpenning, who founded a new company Tesla Motors in 2003 with the aim of building “the most sexy electric sports-car.” The next year Musk joined the company and brought with him the tremendous funding and resources that finally put Tesla Roadster into production, which was debut in 2006 and greeted with such enthusiasms (“Zero to 60 in 4 Seconds, Wicked Fast” by New York Times, “The Best Innovation in 2006” by Time) that put pressure on the major automakers to electrify. One by one, GM, Ford, Toyota, and Nissan joined the game, with varying degrees of electrification (battery-gasoline hybrid, plug-in hybrid, pure battery electric, etc.), gradually turning electric car from expensive toy into a house-hold transportation vehicle. In 2018, the electric vehicle market sees China as the leading manufacturer, which has been driven by the government incentives, with Europe (mainly Germany and France) as the distant second. Li-ion batteries were also brought into the grid-storage market, serving either as load-leveling component for power distribution, or storage component for the energy harvest farms from intermittent sources such as solar or wind farms. As a device that packs electricity most efficiently in the convenient and mobile form, Li-ion battery will undoubtedly continue to be a key part in the future key technological revolutions. While Whittingham, Goodenough, and Yoshino well deserve this Nobel Prize, we should also remember that, as an electrochemical device, Li-ion battery consists of multiple components that must be precisely synchronized to work together, and many scientists and engineers made contributions to make this happen during the lengthy history of its development. Based on the success of Li-ion batteries, the battery and materials scientists are exploring the next battery chemistry that delivers not only higher energy density but also does so with higher safety, enabling better batteries that can further shape our life in this mobile, digital and highly informative age. The author thanks the support from the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Kang Xu obtained his Ph. D. in Chemistry from Arizona State University under the tutelage of Prof. Austen Angell. He has been working on battery electrolyte materials and interphase chemistries for 30+ years. He has published over 250 papers and has been recognized by numerous awards, including the International Battery Association Technology Award (2017) and Electrochemical Society Battery Research Award (2018). In the field he is best known for the two classical reviews published at Chemical Reviews in 2004 and 2014. He is current an ARL Fellow and Team Leader of Extreme Battery Chemistries at the U.S. Army Research Lab. Besides research, he is one of the co-founders of Center of Research on Extreme Batteries (CREB), serves as associate editor for Energy & Environmental Materials and Electrochemistry, Guest-editor of ECS Interface, as well as on Advisory Board of ACS Applied Materials and Interface.