Demand for Li-ion batteries in two decades. Reproduced with permission [3].

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... demand for Li-ion batteries increases rapidly, especially with the demand from electric-powered vehicles (Fig. 1). It is expected that nearly 100 GW hours of Li-ion batteries are required to meet the needs from con- sumer use and electric-powered vehicles with the later takes about 50% of Li-ion battery sale by 2018 [3]. Furthermore, Li-ion batteries will also be employed to buffer the intermittent and fluctuating green energy supply from ...

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... could be suitable for mass production. Interestingly, few monolayers of carbon film formed on the surface of olivine particles and the carbon also was deposited inside the pores of the particles. With just 3.4 wt% carbon, impressive cycling performance over 70 cycles could be achieved with no capacity fade at either room temperature or at 37°C (Fig. 11). It is particularly interest- ing to note that, without addition of carbon black as the conductivity enhancer typically for LiFePO 4 , they could achieve specific capacity of 140 and 150 mAh/g when tested at room temperature and at 37°C, respectively. The improved performance was attributed to the network of carbon film on the surface ...

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... addition to carbon coating, other conductivity en- hancers have been explored to improve the conductivity of LiFePO 4 as well. Chung and colleagues [56] explored the preparation of LiFePO 4 thin films with uniformly dis- persed highly conductive silver to improve the conductivity of LiFePO 4 (Fig. 12). With a small fraction of dispersed silver at only 1.37 wt%, a superior electrochemical per- formance in terms of specific capacity, cyclability, and high charge-discharge rate has been achieved. The preparation procedure for making this uniformly dispersed silver in LiFePO 4 thin films was remarkably simple. Pulsed laser deposition ...

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... could help to increase the energy density but demand for alternative stable electrolyte instead of conventional electrolyte. Another family of emerging polyanionic cathode is Li 2 MSiO 4 , (M = Mn, Fe, Co, Ni, e.g., Li 2 MnSiO 4 ), which could offer much high capacity of 330 mAh/g. The obstacles to adopt those high-capacity Li 2 MSiO 4 ( Fig. 13) are their poor electronic conductivity, poor rate capability and fast capacity fading upon cycling ...

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... oxide (with average composition of Li[Ni 0.68 Co 0.18 Mn 0.18 ] O 2 ) microparticles [59]. The cathode materials is unique in the way that the microparticles have concentration gra- dient, where the core is rich in Ni, and the outer layer is rich in Mn with decreasing Ni concentration and increasing Mn and Co concentrations at the surface (Fig. 14). The bulk core of Ni-rich cathode provides high capacity. The concentration-gradient outer layer and the surface improve the thermal stability. The cathode materials demonstrated impressive high reversible capacity of 209 mAh/g and good safety characteristics. It should be noted that the materials preparation procedure based on copre- ...

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... the first commercializa- tion of carbonaceous anodes, carbon is still dominant in commercial Li-ion batteries today. Graphitic carbon with Figure 13. The crystal structure of (A) a typical form of Li 2 MnSiO 4 (Pmnb) and (B) the hypothetical structure of the fully delithiated MnSiO 4 with SiO 4 shown in blue, LiO 4 in green, and MnO 4 in purple. ...

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... much effort is focused on disordered carbon, although the exact mechanism by which the high- specific capacity is achieved has not been fully understood [67][68][69]. Other carbon-based materials that have been extensively studied are buckminsterfullerene, carbon Figure 15. A family of carbon-based materials with different structure: (A) graphite with a stack of graphene layers, (B) diamond with carbon atoms arranged in a FCC structure, (C) buckminsterfullerene (C 60 ) with consisting of graphene balled into a sphere, (D) carbon nanotube with rolled-up cylinder of graphene, and (E) graphene of a single layer carbon, (F) the schematic of lithium intercalation and deintercalation between graphene layers in graphite. ...

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... and graphane (Fig. 15). Carbon nanotubes, in particular, can be a good lithium host on grounds of their excellent electronic conductivity and other properties associated with their linear dimensionality [70,71]. However, current interest is focused on CNT-and graphene- based composites instead of pristine CNTs or graphene to achieve much higher capacity than ...

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... have been widely studied since the first report by Tarascon's group [31]. Although metal oxides are generally poor in conductivity, properly tailored metal oxides at nanoscale have demonstrated promising charac- teristics. The reaction mechanism of lithiation and delithi- ation in metal oxides can be generally classified into three main types (Fig. 16): (1) the insertion/extraction, (2) the alloying/dealloying, and (3) the conversion mechanisms. The first mechanism is observed in different kinds of anode materials, including anatase TiO 2 [75]. In fact, most of cathode materials with layered or spinel structures also follow the insertion-extraction mechanism as discussed previously. ...

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... facile gram-scale preparation of anatase TiO 2 high- order structures with subunits of tunable nanoparticle aggregates from one precursor for Li-ion batteries has been reported [75]. The nanoparticles were formed by basic building units aggregated controlled by calcination temperature (Fig. 17). Interestingly, the size of the basic building units of TiO 2 nanoparticles can significantly af- fect their electrochemical characteristics. When the crystal- lite size was at 17 nm, the anatase TiO 2 aggregates achieved an impressive high capacity 170 mAh/g, which is close to the theoretical value of 168 mAh/g. When charged at higher ...

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... at nanoscale by simple cost-effective approaches on a large scale. Recently silicon nanowires have been reported to demonstrate promising reversible lithium storage proper- ties [15]. Cui and colleagues [15] proposed and demon- strated that silicon nanowires were superior in lithium ion storage as compared to silicon thin film and particles (Fig. 18). The silicon nanowires could avoid the issue of pulverization and contact loss due to facile strain relaxation and efficient electron transport along each nanowire. Bogart et al. [77] also demonstrated that silicon nanowires with carbon skin could enhance the cycling and rate per- formances of silicon nanowires in lithium storage. ...

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... transport along each nanowire. Bogart et al. [77] also demonstrated that silicon nanowires with carbon skin could enhance the cycling and rate per- formances of silicon nanowires in lithium storage. Recently, in another attempt, Ti@Si core-shell coaxial nanorods were proposed to further improve the electrochemical perfor- mances of Si nanorods (Fig. 19). As compared to pristine Si nanorods, the benefit of metallic core is that the axial resistance observed in solid Si nanorods could be dramati- cally reduced. The electrons released/acquired on electro- chemical reactions of dealloying/alloying for LixSi could be transferred to the Ti foil current collectors easily via the metallic Ti ...

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... author believes that silicon nanomaterials could potentially replace carbon anodes in the next 10 years, Figure 18. Schematic comparing the stability of (B) silicon nanowires with (A) thin film and particles upon repeated lithiation and delithiation. ...

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... in air at 800°C could remove the hollow carbon spheres and compacted the SnO 2 nanoparticles into hollow spheres. However, capacity fading was generally observed in SnO 2 -based anodes [81]. Another interesting SnO 2 -based anode material is electro- spray deposited thin films of particles with unique porous spherical multideck-cage morphology (Fig. 21). The reversible capacity was reported to be as high as 1158 mAh/g, which is even higher than theoretical value. The improved elec- trochemical performance was attributed to the unique struc- ture and the presence of Li 2 O and CuO phases in the composite film [85]. Interestingly, even higher capacity of 2050 mAh/g with excellent ...