The lithium-air battery is one of the most promising technologies among various electrochemical energy storage systems. We demonstrate that a novel air electrode consisting of an unusual hierarchical arrangement of functionalized graphene sheets (with no catalyst) delivers an exceptionally high capacity of 15000 mAh/g in lithium-O(2) batteries which is the highest value ever reported in this field. This excellent performance is attributed to the unique bimodal porous structure of the electrode which consists of microporous channels facilitating rapid O(2) diffusion while the highly connected nanoscale pores provide a high density of reactive sites for Li-O(2) reactions. Further, we show that the defects and functional groups on graphene favor the formation of isolated nanosized Li(2)O(2) particles and help prevent air blocking in the air electrode. The hierarchically ordered porous structure in bulk graphene enables its practical applications by promoting accessibility to most graphene sheets in this structure.

The effects of carbon microstructure and loading on the performance of Li/air batteries were investigated. We found that the capacities of Li/air batteries were related to both the specific capacity per unit weight of the carbon source (mAhnormalg−1) and the carbon locating per unit area (gcm−2) . Therefore, the product of these two parameters [i.e., the area-specific capacity (mAhcm−2) ] was introduced to optimize the performance of the air electrode. At the fixed electrolyte amount (100μL/cell) , the best area-specific capacity of 13.1mAhcm−2 was obtained at a carbon loading of 15.1mgcm−2 . Further increase or decrease in the carbon loading led to a reduced area-specific capacity. The capacities of air electrodes increased with increasing mesopore volumes of the carbon sources. The uniformity of the pore sizes also played an important role in determining the electrochemical performances of the Li/air batteries. At fixed carbon loading and discharge rates, the capacity increased significantly with increasing electrolyte amounts. This phenomenon was explained by the formation of extra triphase regions in the air electrodes. After optimizing the electrode and electrolyte parameters, a high capacity of 1756mAhnormalg−1 carbon was obtained for Li/air batteries operated in ambient oxygen pressure (0.21 atm).

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Lithium ion batteries (LIBs) continuously prove themselves to be the main power source in consumer electronics and electric vehicles. To ensure environmental sustainability, LIBs must be capable of performing well at extreme temperatures, that is, between −40 and 60 °C. In this review, the recent important progress and advances in the subzero and elevated temperature operations of LIBs is comprehensively summarized from a materials perspective. In the scenario of subzero temperatures, limitations, electrolytes, anodes, and solid electrolyte interphase (SEI); cathodes and cathode electrolyte interphase (CEI); and binders are thoroughly discussed to explore the fundamentals and basics that underlie the decay in electrochemical performance and how the chemistry, physics, and electrochemistry are correlated with the materials and components that interact with each other. In the case of high temperatures limitations, the thermal stability of the key materials and components are reviewed, and then the reaction thermodynamics and kinetics of the anodes, cathodes, electrolytes, and their interactions are described using the highest occupied molecular orbit (HOMO)/lowest unoccupied molecular orbit (LUMO), and are extensively discussed. The prospect of combining the extreme temperature poles in a single cell by introducing appropriate electrolytes and additives is discussed.

IntroductionLithium (Li)-ion batteries (LIBs) have now been the indispensable power sources for portable electronic devices, electric vehicles, stationary or grid applications, etc. [1] However, further efforts on extending the cycle life, rate capability, energy density and working temperature range and improving the safety of LIBs are still facing significant challenges for their large-scale applications. Focusing on the increase in energy density of a battery, the possible approach is to use the high capacity electrode (cathode or anode) material and the high voltage cathode material. Ni-rich layered oxides LiNi x Mn y Co 1−x−y O 2 (NMC) with Ni content ≥80% (e.g., NMC811) are regarded as one of the most potential candidates to usher in the new stage of ultra-high energy density LIBs due to their increased specific capacities at higher voltages and the low cost with less Co content. However, the practical applications of these Ni-rich NMC cathode materials are greatly hindered by the poor cathode-electrolyte interface (CEI) layer formed on such cathode surface in the state-of-the-art electrolytes comprised of lithium hexafluorophosphate (LiPF 6 ) in carbonate solvents, especially at voltages higher than 4.3 V versus Li/Li + , [2] causing continuous electrolyte oxidative decomposition and other related side reactions such as transition metal dissolution from the cathode surface, thus leading to poor cycling stability, especially at elevated temperatures and high operating voltages. [3] Therefore, advanced electrolytes with better oxidative protection to Ni-rich NMC cathode materials, especially under high voltages are critically important for enabling application of Ni-rich NMCs in LIBs.Significant efforts have been made to develop novel electrolytes for high voltage cathode materials, mainly through using high anodic solvents to substitute carbonate solvents, the increase of salt concentration and the utilization of film-forming additives. Fan et al. developed an all-fluorinated electrolyte of 1 m LiPF 6 in fluoroethylene carbonate/3,3,3-fluoroethylmethyl carbonate/1,1,2,2-tetrafluoroethyl-2′,2′,2′-trifluoroethyl ether (FEC/FEMC/HFE, 2:6:2 by wt), which significantly enhanced the cycling stability of Li||NMC811 (2.7-4.4 V) and Li||LiCoPO 4 (3.5-5.0 V) in high voltages by effectively inhibiting electrolyte LiNi x Mn y Co 1−x−y O 2 (NMC) cathode materials with Ni ≥ 0.8 have attracted great interest for high energy-density lithium-ion batteries (LIBs) but their practical applications under high charge voltages (e.g., 4.4 V and above) still face significant challenges due to severe capacity fading by the unstable cathode/electrolyte interface. Here, an advanced electrolyte is developed that has a high oxidation potential over 4.9 V and enables NMC811-based LIBs to achieve excellent cycling stability in 2.5-4.4 V at room temperature and 60 °C, good rate capabilities under fast charging and discharging up to 3C rate (1C = 2.8 mA cm −2 ), and superior low-temperature discharge performance down to −30 °C with a ca...