Batteries 4282 5.1. Spinels 4282 5.2. Other Layered Oxides 4283 5.2.1. Mixed Nickel−Cobalt Dioxide, LiNi 1-y Co y O 2 4283 5.2.2. Lithium Manganese Dioxide, LiMnO 2 4283 5.2.3. Mixed Manganese−Cobalt Dioxide, LiMn 1-y Co y O 2 4284 5.2.4. Mixed Nickel−Manganese Dioxide, LiNi 1-y Mn y O 2 sMultielectron Redox Systems 4285 5.2.5. Mixed Nickel−Manganese−Cobalt Dioxide, LiNi 1-y-z Mn y Co z O 2 4287 5.2.6. Lithium-Rich Mixed-Metal Dioxides, Li 1+x M 1-x O 2 4292 5.3. Iron Compounds Including Oxides and Phosphates 4293 5.3.1. Olivine Phase 4293 5.3.2. Other Iron Phosphate Phases 4295 5.3.3. Vanadium Phosphate Phases 4296 6. Conclusions and What Does the Future Hold 4297 7. Abbreviations and Specialized Terms 4297 8. Acknowledgments 4297 9. References 4297

State-of-the-art lithium (Li)-ion batteries are approaching their specific energy limits yet are challenged by the ever-increasing demand of today's energy storage and power applications, especially for electric vehicles. Li metal is considered an ultimate anode material for future high-energy rechargeable batteries when combined with existing or emerging high-capacity cathode materials. However, much current research focuses on the battery materials level, and there have been very few accounts of cell design principles. Here we discuss crucial conditions needed to achieve a specific energy higher than 350 Wh kg −1 , up to 500 Wh kg −1 , for rechargeable Li metal batteries using high-nickel-content lithium nickel manganese cobalt oxides as cathode materials. We also provide an analysis of key factors such as cathode loading, electrolyte amount and Li foil thickness that impact the cell-level cycle life. Furthermore, we identify several important strategies to reduce electrolyte-Li reaction, protect Li surfaces and stabilize anode architectures for long-cycling high-specific-energy cells.

The electrochemical reaction of layered titanium disulfide with lithium giving the intercalation compound lithium titanium disulfide is the basis of a new battery system. This reaction occurs very rapidly and in a highly reversible manner at ambient temperatures as a result of structural retention. Titanium disulfide is one of a new generation of solid cathode materials.

Rechargeable energy storage systems with high energy density and round-trip efficiency are urgently needed to capture and deliver renewable energy for applications such as electric transportation.Lithium-air/lithium-oxygen (Li-O 2 ) batteries have received extraordinary research attention recently owing to their potential to provide positive electrode gravimetric energies considerably higher ($3 to 5Â) than Li-ion positive electrodes, although the packaged device energy density advantage will be lower ($2Â). In light of the major technological challenges of Li-O 2 batteries, we discuss current understanding developed in non-carbonate electrolytes of Li-O 2 redox chemistry upon discharge and charge, oxygen reduction reaction product characteristics upon discharge, and the chemical instability of electrolytes and carbon commonly used in the oxygen electrode. We show that the kinetics of oxygen reduction reaction are influenced by catalysts at small discharge capacities (Li 2 O 2 thickness less than $1 nm), but not at large Li 2 O 2 thicknesses, yielding insights into the governing processes during discharge. In addition, we discuss the characteristics of discharge products (mainly Li 2 O 2 ) including morphological, electronic and surface features and parasitic reactivity with carbon. On charge, we examine the reaction mechanism of the oxygen evolution reaction from Li 2 O 2 and the influence of catalysts on bulk Li 2 O 2 decomposition. These analyses provide insights into major discrepancies regarding Li-O 2 charge kinetics and the role of catalyst. In light of these findings, we highlight open questions and challenges in the Li-O 2 field relevant to developing practical, reversible batteries that achieve the anticipated energy density advantage with a long cycle life. Broader contextLithium-O 2 batteries have received heightened attention in the last ve years owing to an increasing need for high-density energy storage for electric vehicles. Among the available battery chemistries, the Li-O 2 system is, in some regards, one of the most promising. This is largely attributed to a signicant gravimetric energy enhancement compared to Li-ion, with Li-O 2 projected to have at least a factor of two enhancement for a fully packaged battery. However, practical Li-O 2 batteries will only be successfully developed once current battery performance challenges are adequately addressed. Critical challenges include low round-trip efficiency resulting from high charging overpotentials, poor cycle life, and low power. These challenges present exciting opportunities for continued fundamental studies that can pave the way for improving electrode performance. Developing deeper mechanistic understanding of oxygen redox reactions in organic electrolytes, morphological and electronic features of reaction products, and improving the chemical stability of electrode and electrolyte would enable more effective rational design of electrodes and Li-O 2 batteries to meet high expectations for improved performance.