This review is focused on the recent progress and strategies in the fabrication of high performance anode materials for Na-ion batteries.

To develop a long cycle life and good rate capability electrode, 3D hierarchical porous α-Fe 2 O 3 nanosheets are fabricated on copper foil and directly used as binder-free anode for lithium-ion batteries. This electrode exhibits a high reversible capacity and excellent rate capability. A reversible capacity up to 877.7 mAh g −1 is maintained at 2 C (2.01 A g −1 ) after 1000 cycles, and even when the current is increased to 20 C (20.1 A g −1 ), a capacity of 433 mA h g −1 is retained. The unique porous 3D hierarchical nanostructure improves electronic-ionic transport, mitigates the internal mechanical stress induced by the volume variations of the electrode upon cycling, and forms a 3D conductive network during cycling. No addition of any electrochemically inactive conductive agents or polymer binders is required. Therefore, binder-free electrodes further avoid the uneven distribution of conductive carbon on the current collector due to physical mixing and the addition of an insulator (binder), which has benefi ts leading to outstanding electrochemical performance.

Single and binary metal oxides based on conversion reactions for Li-ion batteries are discussed in this review.

Although transition metal oxide electrodes have large lithium storage capacity, they often suffer from low rate capability, poor cycling stability, and unclear additional capacity. In this paper, CoO nanowire clusters (NWCs) composed of ultra-small nanoparticles (≈10 nm) directly grown on copper current collector are fabricated and evaluated as an anode of binder-free lithium-ion batteries, which exhibits an ultra-high capacity and good rate capability. At a rate of 1 C (716 mA g −1 ), a reversible capacity as high as 1516.2 mA h g −1 is obtained, and even when the current density is increased to 5 C, a capacity of 1330.5 mA h g −1 could still be maintained. Importantly, the origins of the additional capacity are investigated in detail, with the results suggesting that pseudocapacitive charge and the higher-oxidation-state products are jointly responsible for the large additional capacity. In addition, nanoreactors for the CoO nanowires are fabricated by coating the CoO nanowires with amorphous silica shells. This hierarchical core-shell CoO@SiO 2 NWC electrode achieves an improved cycling stability without degrading the high capacity and good rate capability compared to the uncoated CoO NWCs electrode.

Designed as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries, exfoliated-SnS2 restacked on graphene is prepared by the hydrolysis of lithiated SnS2 followed by a facile hydrothermal method. Structural and morphological characterizations demonstrate that ultrasmall SnS2 nanoplates (with a typical size of 20-50 nm) composed of 2-5 layers are homogeneously decorated on the surface of graphene, while the hybrid structure self-assembles into a three-dimensional (3D) network architecture. The obtained SnS2/graphene nanocomposite delivers a remarkable capacity as high as 650 mA h g(-1) at a current density of 200 mA g(-1). More impressively, the capacity can reach 326 mA h g(-1) even at 4000 mA g(-1) and remains stable at ∼610 mA h g(-1) without fading up to 300 cycles when the rate is brought back to 200 mA g(-1). The excellent electrochemical performance is attributed to the synergetic effects between the ultrasmall SnS2 and the highly conductive graphene network. The unique structure can simultaneously facilitate Na(+) ion diffusion, provide more reaction sites, and suppress aggregation and volume fluctuation of the active materials during prolonged cycling.

Cathode materials mainly include transition metal oxide compounds, [11][12][13][14][15] polyanionic compounds, [16][17][18][19][20][21][22][23] Prussian blue analogues, and organic materials. [24][25][26][27][28] Among the various cathode materials for SIBs, polyanion-based cathode materials possess stable 3D host framework structure due to strong covalent bonding of oxygen atom in the polyanion polyhedra, resulting in their excellent thermal stability and long cycle life. [29] More importantly, this open 3D framework could provide enough interstitial channels for Na + transit and buffer severe volume change during Na + insertion/extraction. Particularly, NaVPO 4 F has attracted a great deal of interests owing to the low-cost raw materials, safe application, and high working potential. NaVPO 4 F was first proposed by Barker et al., [30] which possesses a tetragonal symmetry structure (space group I4/mmm). The crystal structure is consistent with the sodium aluminum fluorophosphate (Na 3 Al 2 (PO 4 ) 2 F 3 ). When used as cathode for Na-ion batteries, it delivered a discharge capacity of 82 mA h g −1 . However, the capacity faded more than 50% after 30 cycles. To improve the cyclability and rate performance, many strategies, including coating with conductive materials, fabricating pores, and doping alien ions have been attempted. [31][32][33] Although these attempts improve the electrochemical property of NaVPO 4 F in a certain degree, the capacity of the reported NaVPO 4 F materials is far below its theoretical specific capacity and still could not meet the application requirements in Na-storage. The root problem is traditional technology for preparing NaVPO 4 F mainly based on the high-temperature solid-state reaction, sol-gel method, and hydrothermal method, which often produce bulk or micrometer-sized NaVPO 4 F particles with insufficient carbon coating, leading to rapid capacity fading since this structure is unfavorable to electron transfer and the permeation of electrolyte. [31,32,34] Hence, it is significant to enhance the kinetics of Na-ion transfer in NaVPO 4 F. In order to achieve this goal, strategies mainly include decreasing the crystallite size and altering morphology of the material. [7,22,35,36] As far as we know, electrospinning is a versatile technique to prepare various 1D carbon-containing composites and produce flexible membrane, [6,8,[37][38][39] which encourages us to fabricate NaVPO 4 F with novel morphology combined the method of electrospinning to improve its electrochemical performance.Herein, we first synthesized 1D NaVPO 4 F/C nanostructure via an electrospinning method. Such a structure combines a variety of advantages for battery electrodes: (I) the small nanoparticles (≈6 nm) shorten the length of Na-ion transport; (II) NaVPO 4 F has received a great deal of attention as cathode material for Na-ion batteries due to its high theoretical capacity (143 mA h g −1 ), high voltage platform, and structural stability. Novel NaVPO 4 F/C nanofibers are successfully prepared via a feasible el...

is inevitable in Li-CO 2 batteries, [11,12] Li-CO 2 /O 2 batteries, [8,13] and even Li-air batteries. [14] Exception is that the discharge products could be different without the generation of Li 2 CO 3 under specific conditions including protected anodes and effective electrolytes. [15,16] Li 2 CO 3 decomposes to CO 2 when the potential is higher than 3.8 V versus Li/Li + . Notably, O 2 evolution is not detected, as is expected according to the decomposition reaction 2Li 2 CO 3 → 4Li + + 4 e -+ 2CO 2 + O 2 . Instead, superoxide radicals or "nascent oxygen" form during the self-decomposition of Li 2 CO 3 . [12,17] More accurate verification was performed through chemical probes, which qualitatively detected the existence of singlet oxygen ( 1 O 2 ). [18] Parasitic reactions of electrolytes and catalyst degradation were then induced by Li 2 CO 3 oxidation. [12,18] Therefore, efficient air cathodes are expected to change this situation.The introduction of metal nanoparticles could limit side reactions and promote the interaction between Li 2 CO 3 and C. [11,[19][20][21] Beyond this, metal-organic frameworks or surface modified carbon materials also brought unexpected electrochemical performance. [22,23] Therefore, catalysts play important roles in Li-CO 2 batteries. [24][25][26][27][28][29] As mentioned above, self-decomposition of Li 2 CO 3 induced a series of parasitic reactions, and further influenced the stability of catalysts during the operation of Li-CO 2 batteries. Only by clarifying the changes of catalysts in this process can we design more stable Li-CO 2 batteries. In previous reports, mono metal catalysts (Ru, Cu, Au, and Ni) exhibited outstanding activity toward Li-CO 2 batteries and revealed some changes in electrochemical processes. [19][20][21] Nevertheless, there exist shortcomings with mono metal catalysts from materials preparation to electrochemical processes. First, for example, the preparation for monodispersed Ru nanoparticles was often achieved under mild experimental conditions without the generation of stable crystal surfaces, further affecting catalytic activity in Li-CO 2 batteries. [21,30] Second, the incompatibility between the discharge products and mono metal nanomaterials might lead to severe agglomeration and dropping during long cycles. [20,31] In this work, we designed a composite of ruthenium-copper nanoparticles highly co-dispersed on graphene (Ru-Cu-G), and this composite cathode endows Li-CO 2 batteries with low overpotential and excellent cyclability through their synergistic Li-CO 2 batteries are attractive electrical energy storage devices; however, they still suffer from unsatisfactory electrochemical performance, and the kinetics of CO 2 reduction and evolution reactions must be improved significantly. Herein, a composite of ruthenium-copper nanoparticles highly co-dispersed on graphene (Ru-Cu-G) as efficient air cathodes for Li-CO 2 batteries is designed. The Li-CO 2 batteries with Ru-Cu-G cathodes exhibit ultra-low overpotential and can be operated for 100 cycles with ...

Cu nanoparticles highly dispersed onto N-doped graphene may provide new strategies for designing highly efficient cathodes for Li–CO2batteries.