In order to address power and energy demands of mobile electronics and electric cars, Li‐ion technology is urgently being optimized by using alternative materials. This article presents a review of our recent progress dedicated to the anode and cathode materials that have the potential to fulfil the crucial factors of cost, safety, lifetime, durability, power density, and energy density. Nanostructured inorganic compounds have been extensively investigated. Size effects revealed in the storage of lithium through micropores (hard carbon spheres), alloys (Si, SnSb), and conversion reactions (Cr2O3, MnO) are studied. The formation of nano/micro core–shell, dispersed composite, and surface pinning structures can improve their cycling performance. Surface coating on LiCoO2 and LiMn2O4 was found to be an effective way to enhance their thermal and chemical stability and the mechanisms are discussed. Theoretical simulations and experiments on LiFePO4 reveal that alkali metal ions and nitrogen doping into the LiFePO4 lattice are possible approaches to increase its electronic conductivity and does not block transport of lithium ion along the 1D channel.

In this paper, we report that Li can be stored in RuO2 with an unusually high coulombic efficiency. The process involves three electrochemical steps: i) formation of a Ru/Li2O nanocomposite, ii) formation of a Li‐containing surface film, and iii) interfacial deposition of Li within the Ru/Li2O matrix. Corresponding to the storage of 5.6 mole of Li ions per mole of RuO2, a high capacity of 1130 mAh g–1 is achieved. Furthermore, virtually all inserted Li ions can be extracted, corresponding to a nearly 100 % coulombic efficiency at the first cycle. Achieving a complete reversibility for such a Li storage system through complex heterogeneous solid‐state electrochemical reactions is possible because of the formation of nanoscale Ru/Li2O during Li insertion and nano‐RuO2 during Li extraction, in addition to the favorable transport properties of RuO2 itself.

The average increase in the rate of the energy density of secondary batteries has been about 3% in the past 60 years. Obviously, a great breakthrough is needed in order to increase the energy density from the current 210 Wh kg À1 of Li-ion batteries to the ambitious target of 500-700 Wh kg À1 to satisfy application in electrical vehicles. A thermodynamic calculation on the theoretical energy densities of 1172 systems is performed and energy storage mechanisms are discussed, aiming to determine the theoretical and practical limits of storing chemical energy and to screen possible systems. Among all calculated systems, the Li/F 2 battery processes the highest energy density and the Li/O 2 battery ranks as the second highest, theoretically about ten times higher than current Li-ion batteries. In this paper, energy densities of Li-ion batteries and a comparison of Li, Na, Mg, Al, Zn-based batteries, Li-storage capacities of the electrode materials and conversion reactions for energy storage, in addition to resource and environmental concerns, are analyzed.

With the increasing environmental problems caused by conventional energy sources and the gradual depletion of oil resources, clean energy is becoming an important topic for the whole world. As an electrochemical energy storage device, the lithium ion battery, which has the highest energy density among secondary batteries, has been widely used in portable electronic devices, and has also been proposed for use in electric vehicles and large-scale energy storage. [1][2][3] However, the performance of current lithium ion batteries cannot meet the requirements in these areas in terms of high power density, long cycle life, and safety. Graphite is widely used as the anode material for Li-ion batteries. The lithiation potential is below 0.2 V versus Li/Li + . This voltage is close to the lithium stripping voltage, especially at high rate, which may cause a safety issue. In addition, a layer of electronically insulating solid-electrolyte interphase (SEI) is inevitably formed on the surface of graphite below 1.0 V versus Li/Li + . Also the graphite anode undergoes a 9% volume variation during full lithium insertion and extraction. Spinel Li 4 Ti 5 O 12 has a relatively high lithiation voltage plateau at 1.54 V versus Li/Li + , which can avoid the formation of the SEI and is very safe. [ 2 , 3 ] In particular, as a zero-strain insertion material, [ 4 ] it has excellent cycling performance. These features make it a promising anode material for large-scale long-life energy storage batteries. However, Li 4 Ti 5 O 12 has pretty low electronic conductivity (ca. 10 − 13 S cm − 1 ) and moderate Li + diffusion coeffi cient (10 − 9 -10 − 13 cm 2 s − 1 ); [ 5 ] thus the high rate performance is not satifi ed for such applications.The most commonly used strategies to solve this problem are to reduce the particle size [ 6 , 7 ] and to coat conductive materials on the Li 4 Ti 5 O 12 surface. [8][9][10][11] Reducing the particle size decreases the lithium diffusion length; therefore the electroactivity and/or rate capability of electrode materials can be improved. Coating conductive materials on the surface enhances the surface conductivity and the electrical contact in the electrode. Several methods of surface modifi cation on Li 4 Ti 5 O 12 have been developed to increase its electrical conductivity and electrical contact, such as using highly conductive carbon, metal, or metal nitrides. [10][11][12][13] These methods signifi cantly improved the electrochemical performance at high rate, however, most of the processes are either complex or have to be performed at high temperature ( > 600 ° C).Recently, porous electrode materials have attracted much attention because of their large contact surface area with the electrolyte and the possibility of forming a 3D mixed conducting network in which metallized mesopores allow both Li + and e − to migrate rapidly, leading to a superior rate performance. [ 14 ] In the work reported here, an ionic liquid was used as a carbon precursor to form a 3D mixed conducting network in porous Li 4 Ti 5 O...

and TiN with lithium in nonaqueous lithium cells over a wide voltage range ͑0.02-4.3 V͒ at room temperature. In most cases, deep Li uptake occurs via heterogeneous reaction resulting in transformation of MX m (M ϭ transition metal; X ϭ F or O or S or N͒ into a nanocrystalline or amorphous LiX m/n /M composite from which Li can be extracted under restoration of the MX m phase. Thermodynamic and kinetic aspects, especially overpotential and its possible origins for both Li uptake and Li extraction processes, are discussed.

LiCoO 2 is a dominant cathode material for Li-ion batteries due to its high volumetric energy density, which could potentially be further improved by charging to high voltage. Practical adoption of the high-voltage charging is, however, hindered by LiCoO 2 's structural instability at the deeply delithiated state and the associated safety concerns. Here, we achieve stable cycling of LiCoO 2 at 4.6 V (vs. Li/Li +) through trace Ti-Mg-Al co-doping. By using state-of-the-art synchrotron X-ray imaging and spectroscopic techniques, we confirm the incorporation of Mg and Al into the LiCoO 2 lattice, which inhibits the undesired phase transition at voltages above 4.5 V. On the other hand, even in trace amount, Ti segregates significantly at grain boundaries and on the surface, modifying the microstructure of the particles while stabilizing the surface oxygen at high voltage. These dopants contribute though different mechanisms and synergistically promote the cycle stability of LiCoO 2 at 4.6 V.

Sodium-ion batteries have captured widespread attention for grid-scale energy storage owing to the natural abundance of sodium. The performance of such batteries is limited by available electrode materials, especially for sodium-ion layered oxides, motivating the exploration of high compositional diversity. How the composition determines the structural chemistry is decisive for the electrochemical performance but very challenging to predict, especially for complex compositions. We introduce the “cationic potential” that captures the key interactions of layered materials and makes it possible to predict the stacking structures. This is demonstrated through the rational design and preparation of layered electrode materials with improved performance. As the stacking structure determines the functional properties, this methodology offers a solution toward the design of alkali metal layered oxides.

A prototype rechargeable sodium-ion battery using an O3-Na0.90[Cu0.22 Fe0.30 Mn0.48]O2 cathode and a hard carbon anode is demonstrated to show an energy density of 210 W h kg(-1) , a round-trip energy efficiency of 90%, a high rate capability (up to 6C rate), and excellent cycling stability.