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.

Electrolytes and interphases in Li-ion batteries and beyond.

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g−1), low density (0.59 g cm−3) and the lowest negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode). Unfortunately, uncontrollable dendritic Li growth and limited Coulombic efficiency during Li deposition/stripping inherent in these batteries have prevented their practical applications over the past 40 years. With the emergence of post-Li-ion batteries, safe and efficient operation of Li metal anodes has become an enabling technology which may determine the fate of several promising candidates for the next generation energy storage systems, including rechargeable Li–air batteries, Li–S batteries, and Li metal batteries which utilize intercalation compounds as cathodes. In this paper, various factors that affect the morphology and Coulombic efficiency of Li metal anodes have been analyzed. Technologies utilized to characterize the morphology of Li deposition and the results obtained by modelling of Li dendrite growth have also been reviewed. Finally, recent development and urgent need in this field are discussed.

Lithium metal anodes for rechargeable batteries

Energy density is the main property of rechargeable batteries that has driven the entire technology forward in past decades. Lithium-ion batteries (LIBs) now surpass other, previously competitive battery types (for example, lead–acid and nickel metal hydride) but still require extensive further improvement to, in particular, extend the operation hours of mobile IT devices and the driving mileages of all-electric vehicles. In this Review, we present a critical overview of a wide range of post-LIB materials and systems that could have a pivotal role in meeting such demands. We divide battery systems into two categories: near-term and long-term technologies. To provide a realistic and balanced perspective, we describe the operating principles and remaining issues of each post-LIB technology, and also evaluate these materials under commercial cell configurations. Post-lithium-ion batteries are reviewed with a focus on their operating principles, advantages and the challenges that they face. The volumetric energy density of each battery is examined using a commercial pouch-cell configuration to evaluate its practical significance and identify appropriate research directions.

Promise and reality of post-lithium-ion batteries with high energy densities

Solid-state electrolytes are attracting increasing interest for electrochemical energy storage technologies. In this Review, we provide a background overview and discuss the state of the art, ion-transport mechanisms and fundamental properties of solid-state electrolyte materials of interest for energy storage applications. We focus on recent advances in various classes of battery chemistries and systems that are enabled by solid electrolytes, including all-solid-state lithium-ion batteries and emerging solid-electrolyte lithium batteries that feature cathodes with liquid or gaseous active materials (for example, lithium–air, lithium–sulfur and lithium–bromine systems). A low-cost, safe, aqueous electrochemical energy storage concept with a ‘mediator-ion’ solid electrolyte is also discussed. Advanced battery systems based on solid electrolytes would revitalize the rechargeable battery field because of their safety, excellent stability, long cycle lives and low cost. However, great effort will be needed to implement solid-electrolyte batteries as viable energy storage systems. In this context, we discuss the main issues that must be addressed, such as achieving acceptable ionic conductivity, electrochemical stability and mechanical properties of the solid electrolytes, as well as a compatible electrolyte/electrode interface. This Review details recent advances in battery chemistries and systems enabled by solid electrolytes, including all-solid-state lithium-ion, lithium–air, lithium–sulfur and lithium–bromine batteries, as well as an aqueous battery concept with a mediator-ion solid electrolyte.

Lithium battery chemistries enabled by solid-state electrolytes

Physical, chemical and electrochemical properties of pure and doped ceria

Design and fabrication of a 100 W anode supported micro-tubular SOFC stack

A novel high energy density rechargeable lithium/air battery

A water-stable Li metal anode with water-stable lithium-conducting glass ceramics, Li 1+x+y Ti 2-x Al x Si y P 3-y O 12 (LTAP), and a lithium-conducting polymer electrolyte, PEO 18 Li(CF 4 SO 2 ) 2 N (PEO 18 LiTFSI), was proposed as the lithium anode for lithium-air batteries with an aqueous solution at the air electrode. LTAP was unstable when in direct contact with Li metal, and the cell resistance of Li/LTAP/Li rapidly increased as a function of the contact time. The Li/PEO 18 LiTFSI/LTAP/PEO 18 LiTFSI/Li symmetrical cell showed no change in the total resistance (around 800 Ω cm 2 at 60°C) over a period of 1 month. The PEO 18 LiTFSI membrane served as a protective interlayer to suppress the reaction between the water-stable glass ceramics LTAP and Li metal effectively. The Li/PEO 18 LiTFSI/LTAP/aqueous LiCl/Pt air cell showed a stable open-circuit voltage of 3.70 V at 60°C for 2 months. The open-circuit voltage was comparable with that calculated from the cell reaction of 2Li + 1/2O 2 + H 2 O = 2LiOH. The cell exhibited a favorable discharge and charge performance at 0.25 mA cm -2 and 60°C.

Nigel M. Sammes

Papers

Physical, chemical and electrochemical properties of pure and doped ceria

Design and fabrication of a 100 W anode supported micro-tubular SOFC stack

A novel high energy density rechargeable lithium/air battery

Li∕Polymer Electrolyte∕Water Stable Lithium-Conducting Glass Ceramics Composite for Lithium–Air Secondary Batteries with an Aqueous Electrolyte

Novel carbon aerogel-supported catalysts for PEM fuel cell application