[en] The surface of LiMn₂O₄ was coated with a nano-layer of FePO₄ by the co-precipitation method followed by heat treatment at different temperatures in air. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the FePO₄ coatings remained in the amorphous phase from 300 °C to 400 °C, whereas crystalline FePO₄ was obtained above 500 °C. In addition, the diffusion of Fe ions into the LiMn₂O₄ lattice was promoted at higher temperatures. The results of the cycle capacity test showed that 3 wt% FePO₄-coated LiMn₂O₄ heat treated at 400 °C exhibited optimum cyclability, with cycle retention of 90.3% after 100 cycles at elevated temperature (55 °C). The electrochemical impedance spectroscopy (EIS) results indicated that 3 wt%–400 °C FePO₄-coated LiMn₂O₄ showed the lowest charge transfer resistance (R_ct) value and the highest diffusion coefficient of the lithium ion of 9.85E−10 cm² s⁻¹. These results indicated that heat treatment at the proper temperature could maintain FePO₄ in the amorphous phase, thereby facilitating Li ion transport and prevent the detachment of FePO₄ and LiMn₂O₄, which was caused by the diffusion of Fe ions into LiMn₂O₄ lattice

[en] Aqueous rechargeable sodium ion batteries has attracted a lot of interests because of its low cost, huge abundance of sodium resources and promising application for large-scale electric energy storage. Herein, we proposed the carbon-coated Na_3V_2(PO_4)_3 nanocomposite (Na_3V_2(PO_4)_3/C) as a cathode material, which was prepared using a simple sol–gel method. The structure and morphology analyses showed that the highly crystalline Na_3V_2(PO_4)_3 nanoparticle with an average size of 350 nm is well coated by a carbon layer with a thickness of 3 nm. Electrochemical tests showed that at high current rates, the Na_3V_2(PO_4)_3/C cathode exhibited excellent electrochemical performance. Impressively, it delivered a discharge specific capacity of 94.5 mAh/g at 10C (1176 mA/g), 90.5 mAh/g at 15C (1764 mA/g) and 71.7 mAh/g at 20C (2352 mA/g). To the best of our knowledge, the notable rate capability has never been reported before for aqueous sodium ion batteries. The enhanced electrochemical behavior could be attributed to the combined advantages of Na_3V_2(PO_4)_3 nanoparticles and carbon layer in the unique core–shell structure, which improved the intrinsic poor electronic conductivity of Na_3V_2(PO_4)_3 greatly. Our results confirmed the prepared Na_3V_2(PO_4)_3/C nanocomposite should be a promising cathode candidate for aqueous sodium ion batteries. - Highlights: • NVP/C nanocomposite is a novel cathode material for aqueous sodium ion battery. • NVP/C nanocomposite delivered a high discharge specific capacity at high rate. • The characteristics of the unique core–shell structure are discussed in detail

[en] Highlights: • Interconnected agglomerates of nanoparticles are assembled into a porous network. • Both bulk insertion and interfacial storage contribute to the high capacity. • The enlarged voltage window of 0.01–3.0 V is employed firstly. • An ultrathin carbon layer (1 nm thick) helps to avoid the structure instability. • The obtained nanoparticles have a high capacity of 270 mA h g⁻¹ at 300th cycle. - Abstract: Mesoporous anatase TiO₂ nanoparticles coated with an ultrathin layer of amorphous carbon are hydrothermally synthesized. Used as an anode material, it achieves a sustained superior lithium storage performance, presenting a high reversible capacity of 270 mA h g⁻¹ up to 300 cycles at a current density of 30 mA h g⁻¹ in an enlarged voltage window of 0.01–3 V, which is firstly adopted for TiO₂ anode material. Remarkably, the carbon coated TiO₂ nanoparticles can still maintain a capacity of 171 mA h g⁻¹ at 300 mA g⁻¹ after 1000 cycles, and even 93 mA h g⁻¹ at 600 mA g⁻¹ after 1000 cycles. We propose an overall view on the diverse features influencing the electrochemical performance of the high-surface-area mesoporous carbon coated TiO₂ nanoparticles and emphasize that the excellent performance is the synergistic result of the enlarged voltage window, which leads to higher interfacial lithium storage, and the uniform amorphous carbon coverage, which not only improves electrical conductivity, minimizes the direct solid-electrolyte interphase (SEI) formation, but also helps to avoid the structure instability arising from the enlargement of the potential window

[en] Through elaborate design, a new rechargeable lithium ion battery has been developed by comprising a surface-treated Li_1_._2Mn_0_._5_4Ni_0_._1_3Co_0_._1_3O_2 cathode and a nano-structured Li_4Ti_5O_1_2 anode. After precondition Na_2S_2O_8 treatment, the initial coulombic efficiency of Li_1_._2Mn_0_._5_4Ni_0_._1_3Co_0_._1_3O_2 cathode has been significantly increased and can be compatible with that of the nano-structured Li_4Ti_5O_1_2 anode. The optimization of structure and morphology for both active electrode materials result in their remarkable electrochemical performances in respective lithium half-cells. Ultimately, the rechargeable lithium ion full battery consisting of both electrodes delivers a specific capacity of 99.0 mAh g"−"1 and a practical energy density of 201 Wh kg"−"1, based on the total weight of both active electrode materials. Furthermore, as a promising candidate in the lithium ion battery field, this full battery also achieves highly attractive electrochemical performance with high coulombic efficiency, excellent cycling stability and outstanding rate capability. Thus the proposed battery displays broad practical application prospects for next generation of high-energy lithium ion battery. - Highlights: • The Li_1_._2Mn_0_._5_4Ni_0_._1_3Co_0_._1_3O_2 cathode is surface-treated by Na_2S_2O_8. • The nano-sized Li_4Ti_5O_1_2 anode is obtained by a solid-state method. • A new Li_1_._2Mn_0_._5_4Ni_0_._1_3Co_0_._1_3O_2/Li_4Ti_5O_1_2 lithium ion battery is developed. • The battery shows high coulombic efficiency, specific capacity and energy density. • The battery shows high capacity retention rate and good high-rate capability

[en] A carbon-free, three-dimensional network structured material composed of NiCo_2O_4 nanowires and Ni foam was synthesized by a facile method. When applied as the air electrode for the lithium–oxygen battery, the unique network structure enables the surface of nanowires highly accessible to the reactants and facilities the electron transport during the charge/discharge processes. A superior electrochemical performance including low charge overpotential and excellent cyclability are obtained. This work suggests the great potential of the carbon-free NiCo_2O_4@Ni as the air electrodes for lithium–oxygen batteries

[en] Highlights: • Nano-sized Li_4Ti_5O_1_2 with B-doped carbon coating layer is prepared. • Effect of B-dopant amount on electrochemical performance is investigated. • A moderate B-dopant amount much improves rate performance. • BC_3 dopant species are important for improving electronic conductivity of carbon. • B-O dopant species might hamper the charge transfer. - Abstract: A facile method was developed to synthesize B-doped carbon coated nano-sized Li_4Ti_5O_1_2 by using glucose and boric acid mixture as the precursor of coating layer, and the effect of B-dopant amounts on electrochemical performance was investigated in detail. It is demonstrated that B-dopant can efficiently improve the electronic conductivity of carbon-coating layer. According to X-ray photoemission spectroscopy analysis and electrochemical investigation, it is also found that, BC_3 dopant species are important for improving electronic conductivity and electrochemical performance, whereas the B-O dopant species, which increases with the enhancement of B-dopant amount, might hamper the charge transfer on Li"+-insertion process. Therefore, the carbon coated nano-sized Li_4Ti_5O_1_2 with a moderate B-dopant amount exhibits much higher electrochemical performance. For example, with a low carbon content of ∼3 wt. %, the optimized B-doped carbon coated Li_4Ti_5O_1_2 can deliver a capacity of around 90 mAh g"−"1 at a high rate of 20C, which is much higher than that of carbon-coated Li_4Ti_5O_1_2. The achieved result indicates that approach of B-doped carbon coating is an effective method for improving the performance of Li_4Ti_5O_1_2.

[en] Highlights: • Li_1_._2Mn_0_._5_4Ni_0_._1_3Co_0_._1_3O_2 is pre-activated by different amounts of Na_2S_2O_8. • 40 wt% Na_2S_2O_8-treated sample shows the best electrochemical properties. • Appropriate Na_2S_2O_8-treatment alleviates the structure conversion upon cycling. • Subsequent CaF_2 coating further stabilizes the interface structure. - Abstract: To overcome the voltage decay upon cycling and increase the initial coulombic efficiency of the layered Li-rich Mn-based oxides, the double modification combining Na_2S_2O_8 treatment with CaF_2 coating has been first proposed in this study. The precondition Na_2S_2O_8 treatment activates the Li_2MnO_3 phase gently and generates a stabilized three-dimensional spinel structure on the surface of particles, leading to a suppression of surface reaction and structure conversion during the subsequent electrochemical process. The mitigation of phase transformation for Na_2S_2O_8-treated Li_1_._2Mn_0_._5_4Ni_0_._1_3Co_0_._1_3O_2 alleviates the voltage decay and energy density degradation upon long-term charge-discharge cycling. In order to further restrain the capacity loss derived from the HF attack and manganese dissolution, 40 wt% Na_2S_2O_8 treated-sample has been modified by an amorphous CaF_2 layer with nano-scale thickness. The first-reported CaF_2-coated/40 wt% Na_2S_2O_8 treated-Li_1_._2Mn_0_._5_4Ni_0_._1_3Co_0_._1_3O_2 presents excellent electrochemical properties with a high initial coulombic efficiency of 99.2%, a capacity retention rate of 89.2% after 200 cycles and a high-rate capability of 152.1 mAh g"−"1 at 3 C. The double surface modification offers a smart design concept for Li-rich Mn-based oxides to meet the practical requirements for advanced lithium ion batteries in electric vehicles

[en] Graphical abstract: A series of Li_1.2Mn_0.6-x/2Ni_0.2-x/2Fe_xO₂ (x=0, 0.03, 0.06, 0.10) cathode materials has been prepared by a modified Pechini process. The structure and morphology of the obtained materials have been examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The electrochemical properties of Li_1.2Mn_0.6-x/2Ni_0.2-x/2Fe_xO₂ have been characterized systematically and Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ exhibits the best cyclic stability and high-rate capability. The Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ electrode delivers a large reversible discharge capacity of 261.6 mAh g⁻¹ at 0.1C-rate with a high capacity retention rate of 90.9% after 80 cycles. Meanwhile it displays obviously improved rate capability with the capacity of 187.3 mAh g⁻¹ at the 1C-rate and stable cycling performance of 165 mAh g⁻¹ after 150 cycles. The effects of a small amount of Fe doping are explored through ex-situ XRD, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscope (HRTEM), differential capacity vs. voltage (dQ/dV) plots and electrochemical impedance spectroscopy (EIS). The results show stable layered structure and well-crystallized particle surface for Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ electrode in contrast with spinel nanodonmains distribution and amorphous surface region for Li_1.2Mn_0.6Ni_0.2O₂ electrode upon cycling, which account for the outstanding electrochemical performance of Fe doped Li_1.2Mn_0.6Ni_0.2O₂ cathode material. - Highlights: • We report a modified Pechini method to prepare Li_1.2Mn_0.6-x/2Ni_0.2-x/2Fe_xO₂. • Li_1.2Mn_0.585Ni_0.185Fe_0.03 exhibits the best electrochemical performance. • The effects of a small amount of Fe doping have been investigated. • 3% Fe doping restrains phase transformation and amorphous surface layer formation. - Abstract: A series of Li_1.2Mn_0.6-x/2Ni_0.2-x/2Fe_xO₂ (x = 0, 0.03, 0.06, 0.10) cathode materials has been prepared by a modified Pechini process. The structure and morphology of the obtained materials have been examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The electrochemical properties of Li_1.2Mn_0.6-x/2Ni_0.2-x/2Fe_xO₂ have been characterized systematically and Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ exhibits the best cyclic stability and high-rate capability. The Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ electrode delivers a large reversible discharge capacity of 261.6 mAh g⁻¹ at 0.1C-rate with a high capacity retention rate of 90.9% after 80 cycles. Meanwhile it displays obviously improved rate capability with the capacity of 187.3 mAh g⁻¹ at the 1C-rate and stable cycling performance of 165 mAh g⁻¹ after 150 cycles. The effects of a small amount of Fe doping are explored through ex-situ XRD, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscope (HRTEM), differential capacity vs. voltage (dQ/dV) plots and electrochemical impedance spectroscopy (EIS). The results show stable layered structure and well-crystallized particle surface for Li_1.2Mn_0.585Ni_0.185Fe_0.03O₂ electrode in contrast with spinel nanodonmains distribution and amorphous surface region for Li_1.2Mn_0.6Ni_0.2O₂ electrode upon cycling, which account for the outstanding electrochemical performance of Fe doped Li_1.2Mn_0.6Ni_0.2O₂ cathode material

[en] Li-rich cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ is prepared by a sol–gel method and coated with CaF₂ layer via a wet chemical process. The pristine and CaF₂-coated samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). An amorphous nanolayer coating of CaF₂ is obtained on the surface of layered pristine material. The CaF₂-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ material exhibits excellent electrochemical performance. The initial coulombic efficiency is enhanced to 89.6% with high initial discharge capacity of 277.3 mAh g⁻¹ after CaF₂ coating. Galvanostatic charge–discharge tests at 0.2 C display faster activation of Li₂MnO₃ phase and higher capacity retention of 91.2% after 80 cycles for CaF₂-coated material. Meanwhile it also shows higher rate capability with the capacity of 141.5 mAh g⁻¹ at the 3 C-rate and stable cyclic performance above 190 mAh g⁻¹ after 100 cycles at the 1 C-rate. The analysis of dQ/dV plots and electrochemical impedance spectroscopy (EIS) indicates that the obvious improvement of CaF₂ coating is mainly attributed to the accelerated phase transformation from layered phase to spinel phase and stable electrolyte/electrode interfacial structure due to the suppression of the electrolyte decomposition

[en] In this article, we studied the surface noble metal modification on Pd nanoparticles, other than the homogeneous or core-shell structure. The surface modification will lead to the uneven constitution within the nanoparticles and thus more obvious optimization effect toward the catalyst brought by the lattice deformation. The surface of the as-prepared Pd nanoparticles was modified with Ru, Pt or Au by a moderate and green approach, respectively. XPS results confirm the interactive electron effects between Pd and the modified noble metal. Electrochemical measurements show that the surface noble metal modified catalysts not only show higher catalytic activity, but also better stability and durability. The PdM/C catalysts all exhibit good dispersion and very little agglomeration after long-term potential cycles toward ethanol oxidation. With only 10% metallic atomic ratio of Au, PdAu/C catalyst shows extraordinary catalytic activity and stability, the peak current reaches 1700 mA mg"−"1 Pd, about 2.5 times that of Pd/C. Moreover, the PdAu/C maintains 40% of the catalytic activity after 4500 potential cycles. - Highlights: • Pd-based catalysts with complicated exposed facets. • Much enhanced electrocatalytic activity and stability with about 10% noble metal M (M = Ru, Pt, Au) on Pd nanoparticles. • The outstanding electrocatalytic performance of PdAu/C towards ethanol oxidation after the Au modification.