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3 of 43) 1402225 wileyonlinelibrary.comhost matrix is observed and this process is called "topotactic reaction", which is either chemically or thermally reversible; a perfect example is Li-intercalation into a graphite matrix. Such intercalation chemistry has been successfully used in Li-ion batteries for both anode and cathode materials and has also been commercialized (i.e., LiCoO 2 /Li x C 6 and LiFePO 4 /Li x C 6 ). [ 4,5 ] The insertion type materials, i.e., metal oxides have several advantages over graphitic anodes when used in practical cells; these include a negligible amount of ICL, no Li-platting issues, no solvent co-intercalation, no electrolyte decomposition, no SEI required for the safe operation of the cell, it is capable of delivering high power density, and has an easy synthesis protocol. On the other hand, less reversible capacity and higher intercalation potential are the notable setbacks compared to graphite. Although numerous Li-intercalating materials are proposed as possible anodes for LIB applications, few of them have only been tested or commercialized in the "rocking-chair" confi guration, for instance Li 4 Ti 5 O 5 anode. Apart from the mentioned anode, few other insertion type materials have been also evaluated in the rocking-chair confi guration for LIBs. Accordingly, the next section describes the structural and electrochemical performance of various intercalation anodes evaluated in the rocking-chair confi guration. TiO 2The existence of several polymorphs is reported for the case of TiO 2 , but anatase, rutile, brookite, and bronze phases have only been reported for Li-storage. [ 26 ] Reversible insertion of one mole of Li is theoretically possible, independent of the polymorph, with a capacity of ≈335 mAh g −1 . However, variation in the Liinsertion potential and reaction mechanism has been observed for such polymorphs. Easy synthesis protocols, scalability, inexpensiveness, ease of tailoring the desired morphology, and eco-friendliness are other key features for utilizing TiO 2 polymorphs for the construction of Li-ion power packs. [27][28][29] AnataseThe anatase phase is one of the widely investigated polymorphs of TiO 2 for Li-storage. [ 27 ] Theoretically, one mole of Li is possible, but practically only ≈0.5 mole Li is reversible upon cycling. Several research attempts have been carried out to improve the reversible capacity, including utilizing high energy (0 0 1) facets because of their dominant higher surface energy (0.90 J m −2 ) compared to (1 0 0) facets (0.44 J m −2 ) and using thermodynamically more stable (1 0 1) facets (0.53 J m −2 ). [ 30,31 ] Although high Li-reversibility could be achieved for such (0 0 1) facets, capacity fading remains an issue upon cycling. [ 32 ] Li-diffusion co-effi cient ( D Li ) values for anatase phase are in the range of 1 × 10 −17 to 4 × 10 −17 cm 2 s −1 for Li-insertion and extraction processes, respectively. [ 27 ] In the crystal chemistry of the anatase phase, TiO 6 octahedra sharetwo adjacent edges with two other octahedral so that...

Recently, great interest has been aroused in flexible/bendable electronic equipment such as rollup displays and wearable devices. As flexible energy conversion and energy storage units with high energy and power density represent indispensable components of flexible electronics, they should be carefully considered. However, it is a great challenge to fabricate flexible/bendable power sources. This is mainly due to the lack of reliable materials that combine both electronically superior conductivity and mechanical flexibility, which also possess high stability in electrochemical environments. In this work, we report a new approach to flexible energy devices. We suggest the use of a flexible electrode based on free-standing graphene paper, to be applied in lithium rechargeable batteries. This is the first report in which graphene paper is adopted as a key element applied in a flexible lithium rechargeable battery. Moreover graphene paper is a functional material, which does not only act as a conducting agent, but also as a current collector. The unique combination of its outstanding properties such as high mechanical strength, large surface area, and superior electrical conductivity make graphene paper, a promising base material for flexible energy storage devices. In essence, we discover that the graphene based flexible electrode exhibits significantly improved performances in electrochemical properties, such as in energy density and power density. Moreover graphene paper has better life cycle compared to non-flexible conventional electrode architecture. Accordingly, we believe that our findings will contribute to the full realization of flexible lithium rechargeable batteries used in bendable electronic equipments.

Development of an eco-friendly, low cost and high energy density ($700 W h kg À1 ) LiMnPO 4 cathode material became attractive due to its high operating voltage $4.1 V vs. Li falling within the electrochemical stability window of conventional electrolyte solutions and offers more safety features due to the presence of a strong P-O covalent bond. The vacancy formation energy for LiMnPO 4 was 0.19 eV higher than that for LiFePO 4 , resulting in a 10 À3 times-diluted complex concentration, which represents the main difference between the kinetics in the initial stage of charging of two olivine materials. This review highlights the overview of current research activities on LiMnPO 4 cathodes in both native and substituted forms along with carbon coating synthesized by various synthetic techniques. Further, carbon coated LiMnPO 4 was also prepared by a solid-state approach and the obtained results are compared with previous literature values. The challenges and the need for further research to realize the full performance of LiMnPO 4 cathodes are described in detail.

A novel sodium hybrid capacitor (NHC) is constructed with an intercalationtype sodium material [carbon coated-Na 3 V 2 (PO 4 ) 3 , C-NVP] and high surface area-activated carbon derived from an eco-friendly resource cinnamon sticks (CDCs) in an organic electrolyte. This novel NHC possesses a combination of high energy and high power density, along with remarkable electrochemical stability. In addition, the C-NVP/CDC system outperforms present, well-established lithium hybrid capacitor systems in all areas, and can thus be added to the list of candidates for future electric vehicles. A careful optimization of mass balance between electrode materials enables the C-NVP/CDC cell to exhibit extraordinary capacitance performance. This novel NHC produces an energy density of 118 Wh kg −1 at a specifi c power of 95 W kg −1 and retains an energy density of 60 Wh kg −1 with high specifi c power of 850 W kg −1 . Furthermore, a discharge capacitance of 53 F g −1 is obtained from the C-NVP/CDC cell at a 1 mA cm −2 current density, along with 95% capacitance retention, even after 10 000 cycles. The sluggish kinetics of the Na ion battery system is successfully overcome by developing a stable, high-performing NHC system.

This review describes the overall research activities focused on developing high-performance Li-ion batteries (LIBs) fabricated with various TiO 2 polymorphs as insertion anodes. Although several polymorphs of TiO 2 have been reported, only the anatase, rutile, bronze, and brookite phases have proven promising. The bronze phase's lower insertion potential, high reversibility and high current performance makes it an attractive candidate for constructing high power and high energy density Liion power packs. In addition, the bronze phase exhibits superior performance over the conventional, commercialized spinel Li 4 Ti 5 O 12 anodes when coupled with the olivine phase LiFePO 4 . This exceptional behavior of the bronze phase opens new avenues for the development of high power LIBs capable of powering zero emission transportation and grid storage.

In this study, we report a novel route via microwave irradiation to synthesize a bio-inspired hierarchical graphene--nanotube--iron three-dimensional nanostructure as an anode material in lithium-ion batteries. The nanostructure comprises vertically aligned carbon nanotubes grown directly on graphene sheets along with shorter branches of carbon nanotubes stemming out from both the graphene sheets and the vertically aligned carbon nanotubes. This bio-inspired hierarchical structure provides a three-dimensional conductive network for efficient charge-transfer and prevents the agglomeration and restacking of the graphene sheets enabling Li-ions to have greater access to the electrode material. In addition, functional iron-oxide nanoparticles decorated within the three-dimensional hierarchical structure provides outstanding lithium storage characteristics, resulting in very high specific capacities. The anode material delivers a reversible capacity of ~1024 mA · h · g(-1) even after prolonged cycling along with a Coulombic efficiency in excess of 99%, which reflects the ability of the hierarchical network to prevent agglomeration of the iron-oxide nanoparticles.

Novel Li-ion hybrid supercapacitors were developed containing composite cathodes of a conducting polymereither polyaniline (PANI) or polypyrrole (PPy)with Li(Mn 1/3 Ni 1/3 Fe 1/3 )O 2 nanoparticles. Activated carbon (AC) anodes were used in the presence of an organic electrolyte. Using a PANI composite electrode resulted in a cell with outstanding supercapacitive behavior, even at high currents.It showed better cycleability than the cells using a PPy composite electrode or pristine material. The cell with a PANI composite electrode delivered high specific capacitances of 140, 93, and 56 F g À1 at current densities of 0.72, 1.45 and 2.15 A g À1 , respectively. The observed capacitances are the best yet reported for hybrid supercapacitors based on Li-intercalating materials in organic electrolytes. The hybrid supercapacitor containing PANI delivered maximum energy and power densities of 49 W h kg À1 and 3 kW kg À1 , respectively. These results demonstrate the potential of developing polymer-encapsulated, Liintercalating materials for high-performance, Li-ion, hybrid supercapacitors.