Lithium Ion Diffusion Path Research Articles

A comparative study of lithium and sodium storage in CeVO3

Due to the existing of multivalent states, V-based materials are considered ideal candidates for high-capacity lithium ions batteries (LIBs) anode materials. In this paper, we reported a novel anode material, CeVO3, which can be used for both LIBs and sodium ions batteries (SIBs). As anode material for LIBs, CeVO3 exhibits an excellent electrochemical performance that the average reversible discharge capacity of 300 mAh/g can be obtained at 0.1 C rate. As an anode material for SIBs, although the reversible capacity is lower than that for LIBs, the cycle stability and rate performance is obviously improved. At 0.1 C rate, as an anode material for SIBs, the mean capacity fade of CeVO3 is about 0.3% per cycle and with the increase of the current rates, the cycle stability further improved. In addition, using the nudged elastic band method, we calculated the diffusion path and diffusion energy barriers of lithium ions and sodium ions in CeVO3 crystalline where three ions diffusion pathways for SIBs (path 1, path 2 and path 3) can be obtained while for LIBs only one ions diffusion pathway (path 3) be obtained. And we also analyzed their impacts on reversible capacity and cycle stability of CeVO3 as an anode material for both LIBs and SIBs where, due to the single Li ions diffusion path, the reversible capacity of CeVO3 for LIBs decreases faster than that for SIBs with the increase of the current rates.

Fabrication of one-dimensional architecture Bi5Nb3O15 nanowires by electrospinning for lithium-ion batteries with enhanced electrochemical performance

Bismuth-based materials are promising alloy-type materials as lithium-ion batteries (LIBs) anode with a high theoretical capacity of about 385 mAh g−1 (Li3Bi). However, the severe volume change during the charge/discharge process limits their applications in LIBs. Nanostructured design is an effective strategy to relieve the volume change. Here, Bi5Ni3O15 nanowires are designed and fabricated via a sample electrospinning technique. When used as anode material, the Bi5Ni3O15 nanowires exhibit a charge/discharge capacity of 372 and 636 mAh g−1 at current density of 100 mA g−1. After 100 cycles, it still retains a capacity of 267 mAh g−1, revealing a good electrochemical performance. This is mainly attributed to the nanostructured design, which can suppress the pulverization resulting from volume variation during the repeated alloy/dealloy process and offers shorter lithium-ion diffusion path together. In addition, in-situ X-ray diffraction experiments are carried out to explore the phase change and lithium storage mechanism. The exploration of Bi5Ni3O15 nanowires as LIBs anode demonstrates that nanostructured design is an effective approach to improve electrochemical performance of alloy-type anodes, which will speed up the process to develop novel alloy-type anodes.

Effects of Fluorine Doping on Structural and Electrochemical Properties of Li6.25Ga0.25La3Zr2O12 as Electrolytes for Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) are promising technologies with great potential in improving safety and energy density, compared with the traditional liquid based lithium ion batteries. However, the bottleneck of SSLBs lies in the issues of poor interface contact and low electrolyte conductivity. In this work, the crystal structure of garnet-type Li6.25Ga0.25La3Zr2O12 (LGLZO) was engineered more rigidly with subdued atoms displacement by fluorine doping and thus smoother and faster lithium ion diffusion paths are formed. The ionic conductivity of garnet-type electrolyte is significantly increased from 5.43 × 10-4 S/cm to 1.28 × 10-3 S/cm at 25 °C and the activation energy is reduced from 0.33 to 0.28 eV. The solid-state symmetric cell consisting of F doped Li6.25Ga0.25La3Zr2O12 electrolyte and lithium metal has lower resistance and displays stable lithium plating/stripping for over 650 h with smaller overpotentials than those on LGLZO electrolyte. Moreover, the all solid-state lithium battery with F-LGLZO electrolyte and LiFePO4 composite electrode exhibits an improved rate capability, which can still keep 132.9 mAh/g at 1 C. Fluorine substitution in garnet-type electrolyte opens new avenues to design new solid-state electrolytes for practical applications of SSLBs.

Three-Dimensional Porous Hierarchically Architectured Li3VO4 Anode Materials for High-Performance Lithium-Ion Batteries

In this work, a binder-free, self-supported, three-dimensional (3D), porous Li3VO4 (LVO) and the carbon-coated Li3VO4(LVO@C) anode materials are prepared on a Ni-foam disc by the electrostatic spray deposition technique. The deposited materials exhibit a unique morphology with sponge-like 3D porous hierarchical architecture. The novel structure can significantly enhance the surface area of the materials, relax the stress/strain of Li+ insertion/deinsertion, and obviously shorten the diffusion path of lithium ions in the charger/discharge process. The porous nickel-foam substrate can also provide an electric transport network and structural support to the electrode, resulting in very excellent rating and cycling performance. In addition, the coated carbon network can further facilitate the electric transport of the material. As a result, both electrodes show outstanding electrochemical properties, especially the LVO@C electrode. The discharge capacities of LVO@C are 508.8, 424.1, 405, 377.5, and 340.1 mA h g–1 at 0.5, 5, 10, 20, and 30 C, respectively, and the capacity can persist at 399 mA h g–1 without any capacity fading even after 1000 cycles at the current density of 10 C. The excellent properties make these LVO-based materials, especially the carbon-coated LVO composite, a promising anode candidate for the low-cost and high-performance LIBs.

General Synthesis of Uniform Three-Dimensional Metal Oxides/Reduced Graphene Oxide Aerogels by a Nucleation-Inducing Growth Strategy for High-Performance Lithium Storage

Three-dimensional (3D) transition metal oxides/reduced graphene oxide aerogels (TMOs/rGO-G) have received great attention for boosting the performance of alkali-ion batteries owing to abundant active sites and a short lithium-ion diffusion path. In this paper, we designed a general self-assembly strategy for preparing uniform 3D porous TMOs/rGO-G (TMOs = CoO, MnO, Fe2O3) hybrids even with a very high TMOs content (especially >80% for CoO/rGO-G and Fe2O3/rGO-G). This strategy contains successive self-assembly processes: self-assembly nucleation of TMOs on GO nanosheets in N,N-dimethylformamide (DMF)/H2O mixed solvent and 3D reduction-assembly of the obtained precursor for hybrid hydrogels along with nucleation-inducing growth of TMOs. Benefiting from the 3D porous network for fast ion/electron transport and a uniform hybrid between TMOs and rGO with a high TMO content, the 3D TMOs/rGO-G demonstrates an impressive lithium storage performance with both outstanding rate capability and excellent cycling stabil...

Preparation of manganese monoxide@reduced graphene oxide nanocomposites with superior electrochemical performances for lithium-ion batteries

Manganese monoxide (MnO) nanowire@reduced graphene oxide (rGO) nanocomposites are synthesized using a simple hydrothermal method combined with a calcination process. The structural and morphological characterization of the composites indicates that the MnO nanowires homogeneously anchor on both sides of the cross-linked rGO. The nanocomposites exhibit a high surface area of 126.5 m2 g−1. When employed as an anode material for lithium-ion batteries, the nanocomposites exhibit a reversible capacity of 1195 mAh g−1 at a current density of 0.1 A g−1, with a high charge-discharge efficiency of 99.2% after 150 cycles. The three-dimensional architecture of the present materials exhibits high porosity and electron conductivity, significantly shortening the diffusion path of lithium ions and accelerating their reaction with the electrolyte, which greatly improves the lithium-ion storage properties. These excellent electrochemical performances make the composite a promising electrode material for lithium-ion batteries.

Uniform honeycomb-like microspheres constructed with titanium nitride to confine polysulfides for extremely stable lithium-sulfur batteries

Lithium-sulfur batteries are considered the most promising next-generation electrochemical energy storage devices due to their high theoretical energy density. However, their practical application is hindered by the severe shuttle effect of polysulfides and the low conductivity of sulfur cathode. Herein, we design a titanium nitride host with a three-dimensional honeycomb-like structure via a spray drying method, which has the advantages of metallic conductivity and ultrafast anchoring to realize efficient adsorption and conversion of polysulfide. The honeycomb-like architecture can shorten the diffusion path of lithium ions, and buffer the volume change of sulfur, which can improve reaction kinetics and maintain the stability of the material structure. As a result, the sulfur cathode based on titanium nitride host exhibits an excellent cycling performance with a stable capacity of 650.4 mAh g−1 within 500 cycles at 100 mA g−1. The excellent performance shows the importance of designing cathode materials with reasonable structures in lithium sulfur batteries.

Engineering Surface-Binder Interactions in High Energy Density Nanowire Conversion Electrodes for Improved Cycle Life without Fluorinated Additives

High capacity conversion electrode materials – like silicon and germanium – that undergo a large volume change upon lithiation and delithiation, require the formation of a robust solid-electrolyte interphase (SEI) layer, which is critically important to mitigate deleterious irreversible reactions that occur at the electrode-electrolyte interface. Over time, these irreversible reactions at the electrode surface result in capacity fade by decreasing the number of mobile lithium ions within the cell and by creating a more hindered diffusion path for lithium ions as they travel toward the electrode. To combat the recurrence of these irreversible reactions in high-capacity conversion electrode systems, the addition of electrolyte additives, such as fluoroethylene carbonate (FEC), is typically deemed necessary to promote stable cycling and improve capacity retention. The observed improvements associated with the inclusion of these virtually universally employed additives have been previously attributed to fluorinated reductive decomposition products that enable the formation of a robust SEI layer. Clearly, careful control over interfacial chemistry and surface reactions are critical for the design of robust electrochemical systems; however, the surface chemistry of the active material is typically ignored prior to electrode formulation. In most studies of high capacity conversion electrode materials, the surfaces remained unmodified, and the active material is incorporated irrespective of what uncontrolled – potentially oxidized – surfaces happen to be present in the native state. Herein, we systematically investigate the electrochemical cycling of germanium nanowire composite conversion electrodes with controlled surface chemistry, formulated with an array of polymeric binders, both in the presence and in the absence of fluorinated electrolyte additives. We observe that controlled modification of the nanowire electrode surface, when paired with certain binders, dramatically improved germanium nanowire-based electrode cycling retention and longevity. In fact, some of these pairings exhibit improved capacity retention in the absence of the fluorinated additives typically deemed necessary for stable cycling, whereas the addition of the fluorinated additive caused the cell capacity to fade more rapidly. Finally, through careful control of surface chemistry and strategic choice of binder material, we show that germanium nanowire-based conversion electrodes can maintain capacity retention in the complete absence of fluorinated additives, fluorinated electrolytes, and fluorinated binders.

Polymer-chelation synthesis of compositionally homogeneous LiNi1/3Co1/3Mn1/3O2 crystals for lithium-ion cathode

Submicrometer-sized LiNi1/3Co1/3Mn1/3O2 (NCM111) crystals with homogeneous composition are prepared via a polymer-chelation chemical solution process. The complexed chelate agents of ethylenediaminetetraacetic acid (EDTA) and polyethyleneimine (PEI) could chelate all metal ions in one step, with intimate mixing at the atomic level, ensuring a homogeneous ion distribution in the product. The as-prepared NCM111 crystals have a narrow particle size distribution with an average size of 250 nm, which can effectively shorten the lithium ion diffusion path. In addition, the NCM111 crystals majorly consist of electrochemically active {010} facets and low Li+/Ni2+ cation mixing, thus delivering a high reversible discharge capacity of 156.1 mAh g−1 after 100th cycles and good rate capability of 102.7 mAh g−1 at 10 C. Furthermore, it is found that the induction of excess Li could deteriorate the rate capability and increase the Li+ solid-state diffusion resistance. However, Al3+ doping could effectively improve the cycling performance, while Nb5+ doping could increase significantly the discharge capacity as well as rate capability. Owing to the flexibility of the chelating chemistry, the synthesis should be extended to prepare other multicomponent single-crystal cathodes with homogeneous composition and desired substation.

Electrodeposited binder-free NiCo2O4@carbon nanofiber as a high performance anode for lithium ion batteries

Binder-free nickel cobaltite on a carbon nanofiber (NiCo2O4@CNF) anode for lithium ion batteries was prepared via a two-step procedure of electrospinning and electrodeposition. The CNF was obtained by annealing electrospun poly-acrylonitrile (PAN) in nitrogen (N2). The NiCo2O4 nanostructures were then grown on the CNF by electrodeposition, followed by annealing in air. Experimental results showed that vertically aligned NiCo2O4 nanosheets had uniformly grown on the surface of the CNF, forming an interconnected network. The NiCo2O4@CNF possessed considerable lithium storage capacity and cycling stability. It exhibited a high reversible capacity of 778 mAhg−1 after 300 cycles at a current density of 0.25 C (1 C = 890 mAg−1) with an average capacity loss rate of 0.05% per cycle. The NiCo2O4@CNF had considerable rate capacities, delivering a capacity of 350 mAhg−1 at a current density of 2.0 C. The outstanding electrochemical performance can be mainly attributed to the following: (1) The nanoscale structure of NiCo2O4 could not only shorten the diffusion path of lithium ions and electrons but also increase the specific surface area, providing more active sites for electrochemical reactions. (2) The CNF with considerable mechanical strength and electrical conductivity could function as an anchor for the NiCo2O4 nanostructure and ensure an efficient electron transfer. (3) The porous structure resulted in a high specific surface area and an effective buffer for the volume changes during the repeated charge–discharge processes. Compared with a conventional hydrothermal method, electrodeposition could significantly simplify the preparation of NiCo2O4, with a shorter preparation period and lower energy consumption. This work provides an alternative strategy to obtain a high performance anode for lithium ion batteries.

Milled flake graphite/plasma nano-silicon@carbon composite with void sandwich structure for high performance as lithium ion battery anode at high temperature

To reduce the influence from volume expansion of silicon during lithium lithiation/delithiation, milled flake graphite/plasma nano-silicon@carbon (MFG/PNSi@C) composite with void sandwich structure is synthesized by assembling thin MFG (thickness of 150 nm) sheets loading with carbon-coated PNSi (plasma nano-silicon) via a facile spray drying method. The MFG/PNSi@C composite, as lithium ion battery anode, exhibits excellent electrochemical performance at room temperature and displays an outstanding cyclic property even at high temperature. The MFG/PNSi@C electrode delivers reversible capacity of 1141 mAh g−1, and high initial Coulombic efficiency of 84.4%, and capacity retention of 84.1% after 200 cycles at a current density of 0.1 A g−1. Even at the current density of 0.2 and 0.4 A g−1, the reversible capacities of 1168 and 1102 mAh g−1 can be achieved respectively, with the capacity retention of 68.9% and 63.9% after 200 cycles. Even the work temperature goes up 60 °C, the discharge/charge capacities of 832/808 mAh g−1 can be obtained at a current density of 0.1 A g−1. The stable cyclic performance is mainly due to the void sandwich structure of the MFG/PNSi@C composite, which dramatically shortens lithium ion diffusion path and pitch carbon shell can buffer huge volume expansion.

Thick Binder‐Free Electrodes for Li–Ion Battery Fabricated Using Templating Approach and Spark Plasma Sintering Reveals High Areal Capacity

AbstractThe templating approach is a powerful method for preparing porous electrodes with interconnected well‐controlled pore sizes and morphologies. The optimization of the pore architecture design facilitates electrolyte penetration and provides a rapid diffusion path for lithium ions, which becomes even more crucial for thick porous electrodes. Here, NaCl microsize particles are used as a templating agent for the fabrication of 1 mm thick porous LiFePO4 and Li4Ti5O12 composite electrodes using spark plasma sintering technique. These sintered binder‐free electrodes are self‐supported and present a large porosity (40%) with relatively uniform pores. The electrochemical performances of half and full batteries reveal a remarkable specific areal capacity (20 mA h cm−2), which is 4 times higher than those of 100 µm thick electrodes present in conventional tape‐casted Li–ion batteries (5 mA h cm−2). The 3D morphological study is carried out using full field transmission X‐ray microscopy in microcomputed tomography mode to obtain tortuosity values and pore size distributions leading to a strong correlation with their electrochemical properties. These results also demonstrate that the coupling between the salt templating method and the spark plasma sintering technique turns out to be a promising way to fabricate thick electrodes with high energy density.

Mesoporous Li2FeSiO4/C nanocomposites with enhanced performance synthesized from fumed nano silica

Mesoporous Li2FeSiO4/C nanocomposites (LFS-FNS and LFS-NS) were prepared from fumed nano silica (FNS) and nano silica (NS) through facile solid-state reactions, respectively. XRD analysis indicates that the crystalline structures of LFS-FNS and LFS-NS are indexed to monoclinic Li2FeSiO4 of P21. SEM results prove that the particle size of LFS-FNS and FNS (25~40 nm) is smaller than that of LFS-NS and NS, revealing the particle size of Li2FeSiO4/C nanocomposites can be tuned by choosing different silica. TEM further indicates Li2FeSiO4 nanoparticles are uniformly dispersed in the amorphous carbon networking of LFS-FNS. Pore structure analysis indicates the external surface areas of LFS-FNS as well as LFS-NS are 51.4 and 36.1 m2 g−1, indicating the pore properties of mesoporous Li2FeSiO4/C nanocomposites can be controlled by using different silica as silicon resource. The reduced particle size and high external surface area shorten the lithium-ion diffusion path and make LFS-FNS possess better electrochemical performance over LFS-NS. The discharge capacity of LFS-FNS is as high as 172 mA h g−1 at 0.1 C.

Facile synthesis of reduced graphene oxide/NH 4 V 3 O 8 with high capacity as a cathode material for lithium ion batteries

Owing to low-electronic conductivity and long lithium ion diffusion path of NH4V3O8 limit its application for lithium-ion batteries (LIBs). To overcome these limitation, a new nano-composites material of NH4V3O8-based have been successfully fabricated by a facial and environmental friendly approach, without the addition of any other template or surfactant. A facile hydrothermal route is employed to synthesised the reduced graphene oxide(rGO)/NH4V3O8 composites. Results show that the NH4V3O8 nano-belt are well distributed on the surface of rGO nanosheets. The resulted rGO/NH4V3O8 nanocomposites exhibit a high capacity as a cathode material for LIBs in comparison with the bare NH4V3O8. When used as cathode material for LIBs, it delivers a maximum discharge capacity of 253 mAhg−1 at 15 mAg−1, 70 mAhg−1 larger than that of the pristine one. The enhanced electrochemical performance is attributed to the synergetic effects between NH4V3O8 and rGO, such as increased conductivity and shortened lithium ion diffusion path.

Graphene conductive additives for lithium ion batteries: Origin, progress and prospect

This paper gives a critical review on the scientific origin, current research progresses and application prospects of graphene conductive additives applied in lithium-ion batteries (LIBs) and emphasizes that the electron transport (enhancement of electron conductance by graphene) and ion diffusion (steric effect of graphene for ion diffusion) should be considered comprehensively for a real mass application. Due to the high electronic conductivity, two-dimensional planar geometrical structure and the ″most flexible and thinnest″ character, our group proposed that graphene is a very promising conducting additive for LIBs. Through ″plan-to-point″ contact model with active material particles, graphene can improve the electronic conductivity of the electrode laminate with much less addition fraction, and hence enhance the energy density of the LIBs. Therefore, graphene shows much better performance than other types of conductive additives, such as carbon black, conducting graphite and even carbon nanotube. Due to the size difference of active material particles, the optimized addition fraction of graphene is different. For example, 2 wt% of graphene works best for LiFePO4, while the most suitable addition amount of graphene in LiCoO2 is only 1 wt%. At the same time, graphene and conducting carbon black can work together to construct a much more efficient conductive network. This kind of binary conductive additive can build high speed pathway for electron both in long and short distance (that is, electrons can transport in the whole electrode and gain access to the whole surface of the active material particle simultaneously), and further improve the electrochemical performance of active materials. Hence, hybrid material containing graphene and carbon black is fabricated to use directly as a novel binary conductive additive. Other than the improvement of the electron conduction, the introduction of graphene brings a bottleneck for its application in LIBs, which has been reported by our group in 2012 based on a 10 Ah LIB using graphene as conductive additive, that is, the steric effect for lithium ion diffusion. Ion diffusion in the porous electrode will be retarded by planar graphene because it is very hard to penetrate through the hexagonal carbon ring for lithium ions. Many efforts have been made by our group to illustrate this effect. We found that it is the thickness and tortuosity of the electrode laminate that determines and the situation varies with different active material. When it comes to LiFePO4, the ion steric effect is not obvious when the electrode is thin (e.g. thinner than 26 μm). When the electrode sheet is thicker (>39 μm), the rate performance of LiFePO4 becomes worse when the graphene addition increases. However, when it comes to LiCoO2, which is large in particle size, the steric effect from graphene disappears. It can be attributed to the pore tortuosity of the electrode. Since the particle size of LiCoO2 is much larger, the electrode is not as tortuous as that of LiFePO4 electrode. Therefore, ions diffuse easily along the electrode thickness direction. Nevertheless, it should be noted that the steric effect in LiFePO4 electrode can be elimated by introducing pores on the surface of graphene or making ribbon-like graphene to provide more diffusion path for lithium ions in the porous electrode. From the practical points, the dispersion of graphene in the active materials is a vitally important but a tough job. In order to construct an efficient conducting network, graphene should be well dispersed and cover every particle of the active material in the electrode. Agglomeration of graphene will not construct a good conducting network, and even bring adverse effects for the ion diffusion. Normal mixing equipments alone cannot ensure good dispersion of graphene, and ultrasonication is an efficient pre-treatment step. New techniques with higher dispersion efficiency are expected to realize really uniform and monolayered dispersion of graphene in active materials, which is very important for mass application of graphene additives in LIBs.

Toward ultrafast lithium ion capacitors: A novel atomic layer deposition seeded preparation of Li4Ti5O12/graphene anode

High performance composite of nanosized Li4Ti5O12 (LTO) and graphene nanosheets was fabricated using a novel atomic layer deposition (ALD) seeded process incorporated with hydrothermal lithiation for the first time. TiO2 nanoislands as seeds were anchored on graphene by ALD process, triggering the unique structure formation of subsequent LTO. The synergistic effects of nanosized LTO and graphene endow the composite with a short lithium ion diffusion path and efficiently conductive network for electron and ion transport, boosting the excellent reversible capacity, rate capability, and cyclic stability as anode materials for lithium ion capacitors (LICs). The reversible capacity of 120.8mAhg−1 at an extremely high current rate of 100C was achieved successfully, and the electrode can be charged/discharged to about 70% of the theoretical capacity of LTO in 25s. Meanwhile, the composite exhibited excellent cyclic stability of 90% capacity retention at 20C with nearly 100% Coulombic efficiency after 2500 cycles. The sintering treatment after hydrothermal reaction has significant effects on the crystallinity, defect density, microstructure and electrochemical property of the composite, which is also supported by theoretical calculations. The results provide a versatile roadmap for synthesis of high performance LTO based composite and new insights into LICs.

Temperature-Dependent Lithium-Ion Diffusion and Activation Energy of Li1.2Co0.13Ni0.13Mn0.54O2 Thin-Film Cathode at Nanoscale by Using Electrochemical Strain Microscopy.

This paper presents the in situ mapping of temperature-dependent lithium-ion diffusion at the nanometer level in thin film Li1.2Co0.13Ni0.13Mn0.54O2 cathode using electrochemical strain microscopy. The thin-film Li1.2Co0.13Ni0.13Mn0.54O2 cathode exhibits higher lithium-ion diffusivities with increasing temperature, which explains the higher capacity observed in the lithium-ion batteries with a Li-rich cathode at elevated temperature. In addition, the activation energy for lithium-ion diffusion can be extracted in an Arrhenius-type plot at the level of grain structure with the assumption that the ionic movement is diffusion controlled. Compared with the grain interiors, the grain boundaries show relatively lower activation energy; hence, it is the preferred diffusion path for lithium ions. This study has bridged the gap between atomistic calculations and traditional macroscopic experiments, showing direct evidence as well as mechanisms for ionic diffusion for Li-rich cathode material.

Revealing the reaction mechanisms of Li-O2 batteries using environmental transmission electron microscopy.

The performances of a Li-O2 battery depend on a complex interplay between the reaction mechanism at the cathode, the chemical structure and the morphology of the reaction products, and their spatial and temporal evolution; all parameters that, in turn, are dependent on the choice of the electrolyte. In an aprotic cell, for example, the discharge product, Li2O2, forms through a combination of solution and surface chemistries that results in the formation of a baffling toroidal morphology. In a solid electrolyte, neither the reaction mechanism at the cathode nor the nature of the reaction product is known. Here we report the full-cycle reaction pathway for Li-O2 batteries and show how this correlates with the morphology of the reaction products. Using aberration-corrected environmental transmission electron microscopy (TEM) under an oxygen environment, we image the product morphology evolution on a carbon nanotube (CNT) cathode of a working solid-state Li-O2 nanobattery and correlate these features with the electrochemical reaction at the electrode. We find that the oxygen-reduction reaction (ORR) on CNTs initially produces LiO2, which subsequently disproportionates into Li2O2 and O2. The release of O2 creates a hollow nanostructure with Li2O outer-shell and Li2O2 inner-shell surfaces. Our findings show that, in general, the way the released O2 is accommodated is linked to lithium-ion diffusion and electron-transport paths across both spatial and temporal scales; in turn, this interplay governs the morphology of the discharging/charging products in Li-O2 cells.

Template-free synthesis of hierarchical MoO2 multi-shell architectures with improved lithium storage capability

A hierarchical multi-shell structure of MoO2 is synthesized through a template-free one-pot solvothermal method. The relative MoO2 electrode exhibits high reversible specific capacity of 780mAhg−1 after 40cycles, good stability, high capacity retention and improved rate performance in the lithium ion battery application. This material has a unique hierarchical architecture which is a combination of pure hollow structure and core-shell structure. Such a hierarchical multi-shell structure can not only amplify active mass-electrolyte contact area and minimizes lithium ion diffusion path, but also provides a unique interstitial void space to relieve the huge volume change of material. Materials with a hierarchical multi-shell structure are expected to be promising candidates in lithium ion batteries application.

Interfacial engineering of metal oxide/graphene nanoscrolls with remarkable performance for lithium ion batteries

The strong interfacial interaction between graphene nanosheets (GNS) and metal oxides (MO) intensively enhances Li+ diffusion, achieving superior rate capability and excellent cycle stability as such interaction strongly restricts the expansion of MO near the interface during lithiation. However, how to design strong interface between GNS and MO is a challenge. Herein, strong interface was achieved by adding sodium citrate (SC) during the dispersion and mixing process of GO and MO (i.e., Fe3O4, Co3O4 and NiO). The use of SC enables better dispersion of MO particles and allows every MO particle to be attached on the GNS. The discharge capacity of Fe3O4@GNS(SC) was 1882mAhg-1 in the second cycle at 0.1C which is higher than Fe3O4@GNS (1120mAhg−1), and maintained at 1610mAhg−1 after 100 cycles much better than that of Fe3O4@GNS (810mAhg−1). The Fe3O4@GNS(SC) composite material also delivered excellent rate performance of 1035mAhg-1 at 1C, in contrast to Fe3O4@GNS (680mAhg-1). In the case of NiO and Co3O4, the corresponding composites displayed the same tendency as Fe3O4@GNS(SC). These results imply that SC with an oxygen functional group and short carbon chain can ensure a large contact area between MO and GNS and short diffusion path for lithium ions in the active material. This work may pave a way for obtaining GNS-based materials for efficient electrochemical energy storage.