Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li-air (O(2)) and Li-S. The energy that can be stored in Li-air (based on aqueous or non-aqueous electrolytes) and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li-air and Li-S justify the continued research effort that will be needed.

Li-O2 and Li-S batteries with high energy storage.

The Li-S battery has been under intense scrutiny for over two decades, as it offers the possibility of high gravimetric capacities and theoretical energy densities ranging up to a factor of five beyond conventional Li-ion systems. Herein, we report the feasibility to approach such capacities by creating highly ordered interwoven composites. The conductive mesoporous carbon framework precisely constrains sulphur nanofiller growth within its channels and generates essential electrical contact to the insulating sulphur. The structure provides access to Li+ ingress/egress for reactivity with the sulphur, and we speculate that the kinetic inhibition to diffusion within the framework and the sorption properties of the carbon aid in trapping the polysulphides formed during redox. Polymer modification of the carbon surface further provides a chemical gradient that retards diffusion of these large anions out of the electrode, thus facilitating more complete reaction. Reversible capacities up to 1,320 mA h g(-1) are attained. The assembly process is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials.

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/Nat%20Mat8,%20500.pdf

A highly ordered nanostructured carbon–sulphur cathode for lithium–sulphur batteries

Energy-storage technologies, including electrical double-layer capacitors and rechargeable batteries, have attracted significant attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and “load leveling” of renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double-layer capacitors requires a step change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning lithium batteries and electric double-layer capacitors.

Challenges Facing Lithium Batteries and Electrical Double‐Layer Capacitors

Electrical energy storage is one of the most critical needs of 21st century society. Applications that depend on electrical energy storage include portable electronics, electric vehicles, and devices for renewable energy storage from solar and wind. Lithium-ion (Li-ion) batteries have the highest energy density among the rechargeable battery chemistries. As a result, Li-ion batteries have proven successful in the portable electronics market and will play a significant role in large-scale energy storage. Over the past two decades, Li-ion batteries based on insertion cathodes have reached a cathode capacity of ∼250 mA h g(-1) and an energy density of ∼800 W h kg(-1), which do not meet the requirement of ∼500 km between charges for all-electric vehicles. With a goal of increasing energy density, researchers are pursuing alternative cathode materials such as sulfur and O2 that can offer capacities that exceed those of conventional insertion cathodes, such as LiCoO2 and LiMn2O4, by an order of magnitude (>1500 mA h g(-1)). Sulfur, one of the most abundant elements on earth, is an electrochemically active material that can accept up to two electrons per atom at ∼2.1 V vs Li/Li(+). As a result, sulfur cathode materials have a high theoretical capacity of 1675 mA h g(-1), and lithium-sulfur (Li-S) batteries have a theoretical energy density of ∼2600 W h kg(-1). Unlike conventional insertion cathode materials, sulfur undergoes a series of compositional and structural changes during cycling, which involve soluble polysulfides and insoluble sulfides. As a result, researchers have struggled with the maintenance of a stable electrode structure, full utilization of the active material, and sufficient cycle life with good system efficiency. Although researchers have made significant progress on rechargeable Li-S batteries in the last decade, these cycle life and efficiency problems prevent their use in commercial cells. To overcome these persistent problems, researchers will need new sulfur composite cathodes with favorable properties and performance and new Li-S cell configurations. In this Account, we first focus on the development of novel composite cathode materials including sulfur-carbon and sulfur-polymer composites, describing the design principles, structure and properties, and electrochemical performances of these new materials. We then cover new cell configurations with carbon interlayers and Li/dissolved polysulfide cells, emphasizing the potential of these approaches to advance capacity retention and system efficiency. Finally, we provide a brief survey of efficient electrolytes. The Account summarizes improvements that could bring Li-S technology closer to mass commercialization.

Challenges and prospects of lithium-sulfur batteries.

This work reports a quantitative analysis of the shuttle phenomenon in Li/S rechargeable batteries. The work encompasses theoretical models of the charge process, charge and discharge capacity, overcharge protection, thermal effects, self-discharge, and a comparison of simulated and experimental data. The work focused on the features of polysulfide chemistry and polysulfide interaction with the Li anode, a quantitative description of these phenomena, and their application to the development of a high-energy rechargeable battery. The objective is to present experimental evidence that self-discharge, charge-discharge efficiency, charge profile, and overcharge protection are all facets of the same phenomenon.

https://iopscience.iop.org/article/10.1149/1.1806394/pdf

Polysulfide Shuttle Study in the Li/S Battery System

Formation of lithium polysulfides in aprotic media

The purpose of this program is to develop an ambient-temperature Li/S secondary battery. The proposed configuration is Li/organic electrolyte, dissolved S/catalytic electrode or current collector. This battery will have an energy density of 100 Wh/lb, including the weight of cell hardware. Investigations of S solubility and electrochemistry have been undertaken in polar, aprotic nonaqueous solvents, chosen for their stability toward Li. Highest S solubility was achieved if S was dissolved in the form of Li polysulfides, Li/sub 2/S/sub n/. Highest S solubilities were achieved in dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF), where 9--10M S solutions were obtained as Li/sub 2/S/sub 9/-/sub 10/. The solutions of highest S concentrations were most readily prepared through the direct reaction of S/sub 8/ with Li/sub 2/S in the presence of the solvent. The discharge and charge capacities of such solutions, 1--2M in S, were measured galvanostatically between preset limits of 1 and 3.7V (vs. Li). Two plateaus were observed in DMSO, at 2.7V and at 2.2V. Discharge capacities of approximately 0.25 e/sup -//S were observed in THF and in methyl acetate. Recharge generally occurred between 2.5 and 3.0V. In DMSO, experiments showed that S/sub 8/ or S/sub 8//sup -2/ could not be reduced onmore » C below S/sub 4//sup -2/, positive of 1.0V vs. Li/sup +//Li. However, S/sup -2/ and S/sub 4//sup -2/ could be readily oxidized on C up to S/sup -2//sub n greater than 10/, withoutthe formation of (insoluble) S/sub 8/. Only S/sub 8//sup -2/ gave S/sub 8/ precipitation upon oxidation. It was concluded that the cycling capacity of the dissolved Li/sub 2/S cathode was limited by the reduction of S/sup -2//sub n < 4/ on C. Other studies indicate that rechargeability of the negative will not be a special problem. 20 figures, 5 tables.« less

/pdf/low-temperature-lithium-sulfur-secondary-battery-annual-10s0g00jnb.pdf

Low temperature lithium/sulfur secondary battery. Annual progress report, December 1, 1974--December 1, 1975. [Ambient-temperature battery with dissolved S]

F.S. Shuker

Papers

Formation of lithium polysulfides in aprotic media

Low temperature lithium/sulfur secondary battery. Annual progress report, December 1, 1974--December 1, 1975. [Ambient-temperature battery with dissolved S]