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The lithium–sulfur battery (Li–S battery) is a type of
rechargeable battery A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or prima ...
. It is notable for its high
specific energy Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, st ...
. The low
atomic weight Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...
of
lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...
and moderate atomic weight of
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
means that Li–S batteries are relatively light (about the density of water). They were used on the longest and highest-altitude unmanned
solar-powered Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to conve ...
aeroplane flight (at the time) by Zephyr 6 in August 2008. Lithium–sulfur batteries may displace
lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible Intercalation (chemistry), intercalation of Li+ ions into electronically Electrical conductor, conducting solids to store energy. Li-ion batteries are c ...
cells because of their higher energy density and reduced cost. This is due to two factors. First the use of
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
instead of a less energy dense and more expensive substances such as cobalt and/or iron compounds found in
lithium-ion batteries A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible intercalation of Li+ ions into electronically conducting solids to store energy. Li-ion batteries are characterized by higher specific energy, energy ...
. Secondly, the use of metallic lithium instead of intercalating lithium ions allows for much higher energy density, as less substances are needed to hold "lithium" and lithium is directly oxidized. Li–S batteries offer specific energies on the order of 550 Wh/ kg, while lithium-ion batteries are in the range of 150260Wh/kg. Li–S batteries with up to 1,500 charge and discharge cycles were demonstrated in 2017, but cycle life tests at commercial scale and with lean electrolyte have not been completed. As of early 2021, none were commercially available. Issues that have slowed acceptance include the polysulfide "shuttle" effect that is responsible for the progressive leakage of active material from the cathode, resulting in too few recharge cycles. Also, sulfur cathodes have low conductivity, requiring extra mass for a conducting agent in order to exploit the contribution of active mass to the capacity. Volume expansion of the sulfur cathode during S to LiS conversion and the large amount of electrolyte needed are also issues. In the early 2000s, however, scientists began to make progress creating high-stability sulfurized-carbon cathodes and by 2020, scientists at Rice University had demonstrated batteries based on sulfurized carbon cathodes that retained >70% of their capacity after 1000 cycles. In 2023, Zeta Energy, a Texas-based startup, announced that multiple national laboratories had independently verified that its lithium-sulfur batteries based on sulfurized-carbon cathodes were polysulfide shuttle free. The competitive advantages of sulfurized-carbon cathodes (e.g., sulfurized polyacrylonitrile, also known as SPAN) were highlighted by a quantitative analysis performed by researchers at
University of Maryland, College Park The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public university, public Land-grant university, land-grant research university in College Park, Maryland, United States. Founded in 1856, UMD i ...
and
Pacific Northwest National Laboratory Pacific Northwest National Laboratory (PNNL) is one of the United States Department of Energy national laboratories, managed by the Department of Energy's (DOE) Office of Science. The main campus of the laboratory is in Richland, Washington ...
in 2024. Their polysulfide shuttle free feature facilitates proper operation under lean electrolyte conditions (< 3 g·(A·h)−1), which was proved to be extremely crucial to attain the full potential of Li-S batteries. The researchers proposed and analyzed unconventional perspectives on how to further improve both energy density and cycle life, highlighting the importance of a proper electrolyte (i.e., stable, lightweight, and highly Li+-conductive).


History

LiS batteries were invented in the 1960s, when Herbert and Ulam patented a primary battery employing lithium or lithium alloys as anodic material, sulfur as cathodic material and an electrolyte composed of
aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated (in which all ...
saturated
amines In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...
. A few years later the technology was improved by the introduction of organic solvents as PC,
DMSO Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula . This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is ...
and DMF yielding a 2.35–2.5 V battery. By the end of the 1980s a rechargeable LiS battery was demonstrated employing ethers, in particular DOL, as the electrolyte solvent. In 2020 Manthiram identified the critical parameters needed for achieving commercial acceptance. Specifically, Li–S batteries need to achieve a sulfur loading of >5 mg·cm−2, a carbon content of <5%, electrolyte-to-sulfur ratio of <5 μL·mg−1, electrolyte-to-capacity ratio of <5 μL·(mA·h)−1, and negative-to-positive capacity ratio of <5 in pouch-type cells. In 2021, researchers announced the use of a sugar-based anode additive that prevented the release of polysulfide chains from the cathodes that pollute the anode. A prototype cell demonstrated 1,000 charge cycles with a capacity of 700 mAh/g. In 2022, an interlayer was introduced that claimed to reduce polysulfide movement (protecting the anode) and facilitate lithium ion transfer to reduce charge/discharge times. Also that year, researchers employed aramid nanofibers (nanoscale
Kevlar Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s as ...
fibers), fashioned into cell membrane-like networks. This prevented dendrite formation. It addressed polysulfide shuttle by using ion selectivity, by integrating tiny channels into the network and adding an electrical charge. Also in 2022, researchers at
Drexel University Drexel University is a private university, private research university with its main campus in Philadelphia, Pennsylvania, United States. Drexel's undergraduate school was founded in 1891 by Anthony Joseph Drexel, Anthony J. Drexel, a financier ...
produced a prototype lithium-sulfur battery that did not degrade over 4000 charge cycles. Analysis has shown that the battery contained monoclinic gamma-phase sulfur, which has been thought to be unstable below 95 degrees Celsius, and only a few studies have shown this type of sulfur to be stable longer than 20 to 30 minutes. In 2024, researchers at
UC San Diego The University of California, San Diego (UC San Diego in communications material, formerly and colloquially UCSD) is a public land-grant research university in San Diego, California, United States. Established in 1960 near the pre-existing Sc ...
announced the discovery of a novel sulfur–iodine crystalline material that can drastically increase the electrical conductivity of a lithium–sulfur battery’s cathode by 11 orders of magnitude, making it 100 billion times more conductive than crystals made of sulfur alone. Moreover, the new material has self-healing properties which make it possible to repair the damage caused from recharge cycling by heating the new material.


Chemistry

Chemical processes in the Li–S cell include lithium dissolution from the
anode An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...
surface (and incorporation into
alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
polysulfide Polysulfides are a class of chemical compounds derived from anionic chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. The inorganic polysulfides have the general formula . These anions are the conjugate bas ...
salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...
) during discharge, and reverse lithium
plating Plating is a finishing process in which a metal is deposited on a surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderab ...
to the anode while charging.


Anode

At the anodic surface, dissolution of the metallic lithium occurs, with the production of electrons and lithium ions during the discharge and electrodeposition during the charge. The
half-reaction In chemistry, a half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the r ...
is expressed as: :Li <=> Li+ + e- In analogy with lithium batteries, the dissolution / electrodeposition reaction causes over time problems of unstable growth of the solid-electrolyte interface (SEI), generating active sites for the
nucleation In thermodynamics, nucleation is the first step in the formation of either a new Phase (matter), thermodynamic phase or Crystal structure, structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically def ...
and dendritic growth of lithium. Dendritic growth is responsible for the internal short circuit in lithium batteries and leads to the death of the battery itself.


Cathode

In Li–S batteries, energy is stored in the sulfur
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...
(S8). During discharge, the lithium ions in the electrolyte migrate to the cathode where the sulfur is reduced to lithium sulphide (Li2S). The sulfur is reoxidized to S8 during the recharge phase. The semi-reaction is therefore expressed as: :S + 2Li+ + 2e- <=> Li2S (E ° ≈ 2.15 V vs Li / Li+ ) Actually the sulfur reduction reaction to lithium sulphide is much more complex and involves the formation of lithium polysulphides (Li2S''x'', 2 ≤ ''x'' ≤ 8) at decreasing chain length according to: ::S8 \ + \ 2 Li -> Li2S8 ::Li2S8 \ + \ 2 Li \ -> \ Li2S6 \ + \ Li2S2 ::... Over all: ::S8 \ + \ 8 Li \ -> 4 Li2S2 And the final step: ::Li2S2 \ + \ 2 Li \ -> \ 2 Li2S The final product is actually a mixture of Li2S2 and Li2S rather than pure Li2S, due to the slow reduction kinetics at Li2S. This contrasts with conventional lithium-ion cells, where the lithium ions are intercalated in the anode and cathodes. Each sulfur atom can host two lithium ions. Typically, lithium-ion batteries accommodate only 0.5–0.7 lithium ions per host atom. Consequently, LiS allows for a much higher lithium storage density. Polysulfides are reduced on the cathode surface in sequence while the cell is discharging: : → → → → Across a porous diffusion separator, sulfur
polymers A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, b ...
form at the
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...
as the cell charges: : These reactions are analogous to those in the sodium–sulfur battery. The main challenges of LiS batteries is the low conductivity of sulfur and its considerable volume change upon discharging and finding a suitable cathode is the first step for commercialization of LiS batteries. Therefore, most researchers use a carbon/sulfur cathode and a lithium anode. Sulfur is very cheap, but has practically no electroconductivity, 5 S⋅cm−1 at 25°C. A carbon coating provides the missing electroconductivity. Carbon nanofibers provide an effective electron conduction path and structural integrity, at the disadvantage of higher cost. In 2024, researchers announced the discovery of a sulfur–iodine material that can dramatically increase the electrical conductivity of a lithium–sulfur battery’s cathode by 11 orders of magnitude, making it 100 billion times more conductive than crystals made of sulfur alone. One problem with the lithium–sulfur design is that when the sulfur in the cathode absorbs lithium, volume expansion of the LixS compositions occurs, and predicted volume expansion of Li2S is nearly 80% of the volume of the original sulfur. This causes large mechanical stresses on the cathode, which is a major cause of rapid degradation. This process reduces the contact between the carbon and the sulfur, and prevents the flow of lithium ions to the carbon surface. Mechanical properties of the lithiated sulfur compounds are strongly contingent on the lithium content, and with increasing lithium content, the strength of lithiated sulfur compounds improves, although this increment is not linear with lithiation. One of the primary shortfalls of most Li–S cells is unwanted reactions with the electrolytes. While S and are relatively insoluble in most electrolytes, many intermediate polysulfides are not. Dissolving into electrolytes causes irreversible loss of active sulfur. Use of highly reactive lithium as a negative electrode causes dissociation of most of the commonly used other type electrolytes. Use of a protective layer in the anode surface has been studied to improve cell safety, i.e., using
Teflon Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene, and has numerous applications because it is chemically inert. The commonly known brand name of PTFE-based composition is Teflon by Chemours, a spin-off from ...
coating showed improvement in the electrolyte stability, LIPON, Li3N also exhibited promising performance.


Polysulfide "shuttle"

Historically, the "shuttle" effect is the main cause of degradation in a LiS battery. The lithium polysulfide Li2Sx (6≤x≤8) is highly soluble in the common electrolytes used for LiS batteries. They are formed and leaked from the cathode and they diffuse to the anode, where they are reduced to short-chain polysulfides and diffuse back to the cathode where long-chain polysulfides are formed again. This process results in the continuous leakage of active material from the cathode, lithium corrosion, low coulombic efficiency and low battery life. Moreover, the "shuttle" effect is responsible for the characteristic self-discharge of LiS batteries, because of slow dissolution of polysulfide, which occurs also in rest state. The "shuttle" effect in a LiS battery can be quantified by a factor fc (0 < fc < 1), evaluated by the extension of the charge voltage plateau. The factor ''fc'' is given by the expression: fc =\frac where ''ks'', ''qup'', '' tot' and ''Ic'' are respectively the kinetic constant, specific capacity contributing to the anodic plateau, the total sulfur concentration and charge current. In 2022, researchers reported the use of a cathode made from carbon nanofibers. Elemental sulfur was deposited onto the carbon substrate (cf.
physical vapor deposition Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...
), which formed the rare and usually metastable monoclinic γ-Sulfur allotrope. This allotrope reversibly reacts to without the formation of intermediate polysulfides . Therefore, carbonate electrolytes, which commonly react with those polysulfides, can be used instead of the rather dangerous ether based electrolytes (low flash and boiling points). Its initial capacity was 800 Ah/kg (classical LiCoO2/graphite batteries have a cell capacity of 100 Ah/kg). It decayed only very slowly, on average 0.04% each cycle, and retained 658 Ah/kg after 4000 cycles (82%).


Electrolyte

Conventionally, LiS batteries employ a liquid organic electrolyte, contained in the pores of PP separator. The electrolyte plays a key role in LiS batteries, acting both on "shuttle" effect by the polysulfide dissolution and the SEI stabilization at anode surface. It has been demonstrated that the electrolytes based on organic carbonates commonly employed in Li-ion batteries (i.e. PC, EC, DEC and mixtures of them) are not compatible with the chemistry of LiS batteries. Long-chain polysulfides undergo nucleophilic attack on electrophilic sites of carbonates, resulting in the irreversible formation of by-products as
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
,
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...
,
ethylene glycol Ethylene glycol ( IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes: as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
and thiocarbonates. In LiS batteries are conventionally employed cyclic ethers (as DOL) or short-chain ethers (as DME) as well as the family of glycol ethers, including DEGDME and TEGDME. One common electrolyte is 1M LiTFSI in DOL:DME 1:1 vol. with 1%w/w di LiNO3 as additive for lithium surface passivation.


Safety

Because of the high potential energy density and the nonlinear discharge and charging response of the cell, a
microcontroller A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...
and other safety circuitry is sometimes used along with
voltage regulator A voltage regulator is a system designed to automatically maintain a constant voltage. It may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism or electronic components. Depending on the ...
s to manage cell operation and prevent rapid discharge.


Lifespan

Lithium-sulfur (Li-S) batteries have a shorter lifespan compared to traditional Li-ion batteries. Recent advancements in materials and
electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...
formulations have shown potential to extend its
cycle life A charge cycle is the process of charging a rechargeable battery and discharging it as required into a load. The term is typically used to specify a battery's expected life, as the number of charge cycles affects life more than the mere passage o ...
to over 1,000 cycles. One of the primary factors limiting the lifespan of Li-S batteries is the dissolution of polysulfides in the
electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...
, which leads to the shuttle effect and results in capacity loss over time. The operating temperature and cycling rate also play significant roles in determining the lifespan of Li-S batteries.


Research


Commercialization

As of 2021 few companies had been able to commercialize the technology on an industrial scale. Companies such as Sion Power have partnered with
Airbus Defence and Space Airbus Defence and Space is a division of Airbus SE. Formed in 2014 in the restructuring of European Aeronautic Defence and Space (EADS), Airbus SE comprises the former Airbus Military, Astrium, and divisions. Contributing 21% of Airbus reven ...
to test their lithium sulfur battery technology. Airbus Defense and Space successfully launched their prototype High Altitude Pseudo-Satellite (HAPS) aircraft powered by solar energy during the day and by lithium sulfur batteries at night in real life conditions during an 11-day flight. The batteries used in the test flight utilized Sion Power's LiS cells that provide 350 W⋅h/kg. Sion originally claimed to be in the process of volume manufacturing with availability by end of 2017; however more recently it can be seen that they have dropped work on their lithium sulfur battery in favor of a lithium-metal battery. British firm OXIS Energy developed prototype lithium sulfur batteries. Together with
Imperial College London Imperial College London, also known as Imperial, is a Public university, public research university in London, England. Its history began with Prince Albert of Saxe-Coburg and Gotha, Prince Albert, husband of Queen Victoria, who envisioned a Al ...
and
Cranfield University Cranfield University is a postgraduate-only public research university in the United Kingdom that specialises in science, engineering, design, technology and management. Cranfield was founded as the College of Aeronautics (CoA) in 1946. Throug ...
, they published equivalent-circuit-network models for its cells. With Lithium Balance of Denmark they built a prototype scooter battery system primarily for the Chinese market, which had a capacity of 1.2kWh using 10Ah Long Life cells, and weighed 60% less than lead acid batteries with a significant increase in range. They also built a 3U, 3,000W⋅h Rack-Mounted Battery that weighed only 25kg and was said to be fully scalable. They claimed their Lithium-Sulfur batteries would cost about $200/kWh in mass production. However, the firm entered bankruptcy (insolvency) status in May 2021.
Sony is a Japanese multinational conglomerate (company), conglomerate headquartered at Sony City in Minato, Tokyo, Japan. The Sony Group encompasses various businesses, including Sony Corporation (electronics), Sony Semiconductor Solutions (i ...
, which also commercialized the first lithium-ion battery, planned to introduce lithium–sulfur batteries to the market in 2020, but has provided no updates since the initial announcement in 2015. Monash University's Department of Mechanical and Aerospace Engineering in Melbourne, Australia developed an ultra-high capacity Li–S battery that has been manufactured by partners at the Fraunhofer Institute for Material and Beam Technology in Germany. It is claimed the battery can provide power to a smartphone for five days. In 2022, the German company Theion claimed to introduce lithium–sulfur batteries for mobile devices in 2023 and for vehicles by 2024. In January 2023,
Houston, Texas Houston ( ) is the List of cities in Texas by population, most populous city in the U.S. state of Texas and in the Southern United States. Located in Southeast Texas near Galveston Bay and the Gulf of Mexico, it is the county seat, seat of ...
company Zeta Energy was awarded $4 million by the
United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...
ARPA-E ARPA-E, or Advanced Research Projects Agency–Energy is an agency within the United States Department of Energy tasked with funding the research and development of advanced energy technologies. The goal of the agency is to improve U.S. economic ...
program to advance its lithium-sulfur batteries based on a sulfurized-carbon cathode and a vertically-aligned carbon nanontube anode. In June 2023,
San Jose, California San Jose, officially the City of San José ( ; ), is a cultural, commercial, and political center within Silicon Valley and the San Francisco Bay Area. With a city population of 997,368 and a metropolitan area population of 1.95 million, it is ...
company Lyten started up a pilot production line making about 100 batteries a day. In 2024, Lyten announced plans a billion-dollar gigafactory in Reno, Nevada, to build up to 10 gigawatt-hours of lithium–sulfur batteries annually.


See also

*
List of battery types This list is a summary of notable electric battery types composed of one or more electrochemical cells. Three lists are provided in the table. The primary (non-rechargeable) and secondary (rechargeable) cell lists are lists of battery chemistry. ...


References


External links

* * *
"EEMB Battery"
EEMB Battery. Retrieved 2018-04-13. {{DEFAULTSORT:Lithium-sulfur battery Rechargeable batteries Metal-sulfur batteries Lithium-ion batteries