LiNi0.5Co0.2Mn0.3O2 positive electrode materials of lithium ion battery can release a discharge capacity larger than 200 mAh/g at high potential (>4.30 V). However, its inevitable capacity fading, which is greatly related to the structural evolution, reduces the cycling performance. The origin of this capacity fading is investigated by coupled in situ XRD-PITT-EIS. A new phase of NiMn2O4 is discovered on the surface of the LiNi0.5Co0.2Mn0.3O2 upon charging to high voltage, which blocks Li+ diffusion pathways. Theoretical calculations predict the formation of cubic NiMn2O4. Moreover, corrosion, cracks, and microstress appear to increase the difficulty of Li+ transportation, which are attributed to the protection degradation of the interfacial film on the positive electrode material at high voltage. After 50 electrochemical cycles, the increase in degree of crystal defects by low-angle grain boundary, evidenced through HR-TEM, leads to poor Li+ kinetics, which in turn causes capacity loss. The in situ XRD-PITT-EIS technique can bring multiperspective insights into fading mechanism of the high-voltage positive electrode materials and provide a solution to control or suppress the problem on the basis of structural, kinetic, and electrochemical interfacial understandings.Keywords: capacity fade; high voltage; in situ XRD-PITT-EIS; LiNi0.5Co0.2Mn0.3O2; NiMn2O4;

Li3VO4 has been regarded as a new-type anode of lithium-ion batteries in recent years, which has a high theoretical specific capacity of 394 mAh g–1, a proper potential for Li+ insertion/deinsertion (∼1 V), and a good rate capacity. However, its low initial Coulombic efficiency, poor conductivity, and poor cycle performance restricts its development. In order to figure out the cause of the low initial Coulombic efficiency of Li3VO4 material, the nanosized Li3VO4 material was synthesized by citric acid-assisted sol–gel method. The lithium storage behaviors of the prepared Li3VO4 material were studied by in-situ XRD and in-situ EIS techniques. In-situ XRD results indicated that there was irreversible phase transformation of Li3VO4 during the initial charging/discharging process. In-situ EIS experiment was performed during the potentiostatic intermittent titration technique (PITT) process to discuss the formation of the solid electrolyte interface (SEI) on the Li3VO4 and the kinetics of lithium-ion diffusion. It is worth pointing out that this is the first time to prove the existence of SEI on Li3VO4 during the initial charging/discharging process by in-situ EIS experiment. It turned out that the irreversible phase transformation and the formation of SEI on Li3VO4 were the two important reasons causing the low initial Coulombic efficiency of Li3VO4 material.Keywords: in-situ EIS; in-situ XRD; low initial Coulombic efficiency; nanosized Li3VO4; PITT

The formation of a spinel cubic framework is identified as a main trigger for the decreasing of the voltage profile for the high-voltage Li-rich manganese-based layered oxide, known as “voltage fade”. This dropping of the operating potential could cause massive loss in the energy density in lithium ion battery systems. To apply a profound understanding into the formation of a spinel cubic phase in Li1.2Ni0.12Co0.15Mn0.53O2 oxide, high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and galvanostatic intermittent titration technique (GITT) are employed. At different states of the initial electrochemical charge process, we found that the spinel cubic region mostly appears in the crystal defective area. The proportion of the spinel phase corresponds well to the Williamson–Hall type microstress value. At 4.70 V charged state, the Inverse Fast Fourier Transform (IFFT) graph shows structural transformation from an O3-type rhombohedral phase to a spinel cubic framework forced by stressful squeezing. The variations in occupation of lithium and manganese ions in the tetrahedral sites (Litetra and Mntetra), and the kinetic performances indicate two forms in the O3-spinel transition: “Li–Mn dumbbell” and spinel nucleus. These experimental results clarify the correlation between the formation of a spinel phase and microstress in Li-rich layered oxides and provide a possible way to depress voltage fade through compromising the crystal defects of the layered oxide.

The nanostructured mixture of a Sn2Fe and Sn2Co alloy composite with uniform cubic shaped particles has been synthesized by a reduction-thermal diffusion alloying reaction. The textural properties of the as-prepared samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. Compared with the Sn2Fe alloy, the alloy composite exhibits better reversibility and cycle performance. At a charge/discharge current density of 50 mA g−1, a reversible capacity of 510 mA h g−1 can be maintained after 50 cycles, and its capacity in the 50th cycle was retained at ca. 85% of that in the second cycle. When the current density is increased to 1000 mA g−1, a reversible capacity of 443 mA h g−1 can be still obtained. The ab initio simulation results indicate that Sn2Fe and Sn2Co have similar crystal structures, demonstrating that the two kinds of alloys can be mixed uniformly by the thermal diffusion alloying reaction. The superior electrochemical performance can be attributed to the homogeneously dispersed inactive metallic material (Fe and Co) nanostructure, which partly accommodates the volume change and also retains the integrity of the active material and matrix, resulting in good cycle performance of the composite electrode.

•Hierarchical waxberry-like NiO has been synthesized by hydrothermal reaction.•Two-dimensional XRD (XRD2) was used to ensure the composition of precursor.•The NiO-300 delivers a charge capacity of 597.8 mAh g−1 cycled 100 weeks at 0.7C.•The superior electrochemical performance should be owed to waxberry-like structure.This work reports a facile synthesis of hierarchical NiO microspheres with a waxberry-like structure by one-pot hydrothermal reaction followed by thermal annealing. We detected the composition of precursor by using two-dimensional detector X-ray diffractometer (XRD2). In addition, XRD, TG, SEM, TEM and BET measurement were used to characterize the structural properties of the as-prepared materials. The XRD result showed that the precursor has been completely transformed into NiO materials by calcination at 300 °C (denoted as NiO-300). Moreover, thanks to the well conservation of hierarchical structure consisting of needle-like nanoparticles in NiO-300 sample, the charge capacity can be stabilized at 597.8 mAh g−1 reversibly when cycled 100 times at a relatively high current density of 0.7C which show a very competitive capacity compared with other nano-structure NiO materials and commercial NiO material. It also showed high rate capability, the reversible charge capacity is still retained to 370.3 mAh g−1, even for the condition of 4.46C (high rate). This NiO-300 material's superior electrochemical performance should be exclusively attributed to the well conserved hierarchical waxberry-like structures, which shortens the diffusion pathways of lithium ions and electrons transfer as well as accommodate the drastic volume change during electrochemical charge/discharge process.

In this work, the Li-rich oxide Li1.23Ni0.09Co0.12Mn0.56O2 was synthesized through a facile route called aqueous solution-evaporation route that is simple and without waste water. The as-prepared Li1.23Ni0.09Co0.12Mn0.56O2 oxide was confirmed to be a layered LiMO2–Li2MnO3 solid solution through ex situ X-ray diffraction (ex situ XRD) and transmission electron microscopy (TEM). Electrochemical results showed that the Li-rich oxide Li1.23Ni0.09Co0.12Mn0.56O2 material can deliver a discharge capacity of 250.8 mAhg–1 in the 1st cycle at 0.1 C and capacity retention of 86.0% in 81 cycles. In situ X-ray diffraction technique (in situ XRD) and ex situ TEM were applied to study structural changes of the Li-rich oxide Li1.23Ni0.09Co0.12Mn0.56O2 material during charge–discharge cycles. The study allowed observing experimentally, for the first time, the existence of β-MnO2 phase that is appeared near 4.54 V in the first charge process, and a phase transformation of the β-MnO2 to layered Li0.9MnO2 is occurred in the initial discharge process by evidence of in situ XRD pattrens and selected area electron diffraction (SAED) patterns at different states of the initial charge and discharge process. The results illustrated also that the variation of the in situ X-ray reflections during charge–discharge cycling are clearly related to the changes of lattice parameters of the as-prepared Li-rich oxide during the charge–discharge cycles.Keywords: aqueous solution evaporation; in situ XRD; layered Li0.9MnO2; Li-rich layered oxide; β-MnO2;

Li-rich layered oxide 0.5Li2MnO3·0.5LiNi0.292Co0.375Mn0.333O2 was prepared by an aqueous solution–evaporation route. X-ray powder diffraction (XRD) showed that the as-synthesized material was a solid solution consisting of layered α-NaFeO2-type LiMO2 (M = Ni, Co, Mn) and monoclinic Li2MnO3. The superlattice spots in the selected area electron diffraction pattern indicated the ordering of lithium ions with transition metal (TM) ions in TM layers in this Li-rich layered oxide. Electrochemical performance testing showed that the as-synthesized material could deliver an initial discharge capacity of 267.7 mAh/g, with a capacity retention of 88.5% after 33 cycles. A new combination technique, multipotential step in situ XRD (MPS in situ XRD) measurement, was applied for the first time to investigate the Li-rich layered oxide. Using this approach, the relationships between kinetics and structural variations can be obtained simutaneously. In situ XRD results showed that the c parameter decreased from 3.70 to 4.30 V and increased from 4.30 to 4.70 V, whereas the a parameter underwent a decrease above 4.30 V during the first charge process. Below 3.90 V during the first discharge process, a slight decrease in the c parameter was found along with an increase in the a parameter. During the first charge process, the value of the coefficient of diffusion for lithium ions (DLi+) decreased to its mininum at 4.55 V, which might be associated with Ni2+ migration, as indicated by both Ni occupancy in 3b sites (Ni3b%) in the Li+ layers and complicated chemical reactions. Remarkably, a lattice distortion might occur within the local domain in the host stucture during the first discharge process, indicated by a slight splitting of the (003) diffraction peak at 3.20 V.Keywords: in situ XRD; Li-rich layered oxide; lithium diffusion; multipotential step; Ni migration

The β-Co(OH)2 sheets with uniform hexagonal shape were prepared using NaBH4 as the structure directing agent at room temperature. After thermal annealing in air at 450 °C for 2 h, the as-prepared β-Co(OH)2 sheets were converted into porous Co3O4 with the hexagonal sheet-like morphology (H-Co3O4). The textural properties of the as-prepared samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. The results of lithium storage capability indicate that the H-Co3O4 electrode exhibits excellent cycleability and rate capacity. At a charge/discharge current density of 50 mA g−1, a reversible capacity of 914 mAh g−1 can be maintained after 40 cycles. When the current density is increased to 1600 mAh g−1, a reversible capacity of 800 mAh g−1 can be still obtained. The superior electrochemical performance is attributed to the porous 2D structures with a finite lateral size and enhanced open-edges, which facilitate Li-ion and electron diffusion through active materials.Highlights► The β-Co(OH)2 hexagonal sheets have been successfully synthesized at room temperature. ► The Co(OH)2 can be easily transformed into porous Co3O4 hexagonal sheets through annealing. ► These porous Co3O4 sheets exhibit excellent cyclic performance and high rate capacity.

This paper reports the facile synthesis of a unique interleaved expanded graphite-embedded sulphur nanocomposite (S-EG) by melt-diffusion strategy. The SEM images of the S-EG materials indicate the nanocomposites consist of nanosheets with a layer-by-layer structure. Electrochemical tests reveal that the nanocomposite with a sulphur content of 60% (0.6S-EG) can deliver the highest discharge capacity of 1210.4 mAh g−1 at a charge–discharge rate of 280 mA g−1 in the first cycle, the discharge capacity of the 0.6S-EG remains as high as 957.9 mAh g−1 after 50 cycles of charge–discharge. Furthermore, at a much higher charge–discharge rate of 28 A g−1, the 0.6S-EG cathode can still deliver a high reversible capacity of 337.5 mAh g−1. The high sulphur utilization, excellent rate capability and reduced over-discharge phenomenon of the 0.6S-EG material are exclusively attributed to the particular microstructure and composition of the cathode.

Nanostructured Cu2Sb @C material was prepared through a simple polyol approach. Hollow Cu2Sb@C core–shell nanoparticles were obtained by controlling the amount of CuCl2 and time of replacement reaction. The hollow Cu2Sb@C nanoparticle electrode showed excellent cycling performance.

Polyvinyl alcohol (PVA) was used as a hydrogen bond functionalizing agent to modify multi-walled carbon nanotubes (CNTs). Nanoparticles of Fe3O4 were then formed along the sidewalls of the as-modified CNTs by the chemical coprecipitation of Fe2+ and Fe3+ in the presence of CNTs in an alkaline solution. The structure and electrochemical performance of the Fe3O4/CNTs nanocomposite electrodes have been investigated in detail. Electrochemical tests indicated that at the 145th cycle, the CNTs–66.7 wt.%Fe3O4 nanocomposite electrode can deliver a high discharge capacity of 656 mAh g−1 and stable cyclic retention. The improvement of reversible capacity and cyclic performance of the Fe3O4/CNTs nanocomposite could be attributed to the nanosized Fe3O4 particles and the network of CNTs.

A new ternary Sn–Ni–P alloy rods array electrode for lithium-ion batteries is synthesized by electrodeposition with a Cu nanorods array structured foil as current collector. The Cu nanorods array foil is fabricated by heat treatment and electrochemical reduction of Cu(OH)2 nanorods film, which is grown directly on Cu substrate through an oxidation method. The Sn–Ni–P alloy rods array electrode is mainly composed of pure Sn, Ni3Sn4 and Ni–P phases. The electrochemical experimental results illustrate that the Sn–Ni–P alloy rods array electrode has high reversible capacity and excellent coulombic efficiency, with an initial discharge capacity and charge capacity of 785.0 mAh g−1 and 567.8 mAh g−1, respectively. After the 100th discharge–charge cycling, capacity retention is 94.2% with a value of 534.8 mAh g−1. The electrode also performs with an excellent rate capacity.

A novel ternary Sb–Co–P alloy electrode was prepared by electroplating on copper current collector as a promising negative electrode material for lithium-ion batteries. The structural and morphological features of the Sb–Co–P alloy were characterized by powder X-ray diffraction (XRD) and scanning electron microscope (SEM). The as-prepared alloy electrode exhibits a high specific capacity and an excellent cycleability. The initial discharge and charge capacities of the Sb–Co–P alloy anode were measured 700 and 539 mA h g−1, respectively. The results suggest that the Sb–Co–P alloy material obtained by the electrodeposition shows a good candidate anode material for lithium-ion batteries.

Nanoparticles of Sn–Co alloy were deposited on the surface of multi-walled carbon nanotubes (CNTs) by reductive precipitation of solution of chelating metal salts within a CNTs suspension. The Sn–Co/CNTs nano-composite revealed a high reversible capacity of 424 mA h g−1 and stable cyclic retention at 30th cycle. The improvement of reversible capacity and cyclic performance of the Sn–Co/CNTs composite is attributed to the nanoscale dimension of the Sn–Co alloy particles and the network of CNTs. Inactive Co as glue matrix of Sn prevents the possible pulverization of nanosized alloy particles. The CNTs could be pinning the Sn–Co alloy particles on their surfaces so as to hinder the agglomeration of Sn–Co alloy particles, while maintaining electronic conduction as well as accommodating drastic volume change during Li insertion and extraction reactions.

Porous Sn–Co–P alloy with reticular structure were prepared by electroplating using copper foam as current collector. The structure and electrochemical performance of the electroplated porous Sn–Co–P alloy electrodes were investigated in detail. Experimental results illustrated that the porous Sn–Co–P alloy consists of mainly SnP0.94 phase with a minor quantity of Sn and Co3Sn2. Galvanostatic charge–discharge tests of porous Sn–Co–P alloy electrodes confirmed its excellent performances: at 50th charge–discharge cycle, the discharge specific capacity is 503 mAh g−1 and the columbic efficiency is as high as 99%. It has revealed that the porous and multi-phase composite structure of the alloy can restrain the pulverization of electrode in charge/discharge cycles, and accommodate partly the volume expansion and phase transition, resulting in good cycleability of the electrode.

The three-dimensional porous Fe–Sb–P amorphous alloy electrodes were prepared by electroplating on porous copper current collector. The structure and electrochemical performance of the electroplated Fe–Sb–P amorphous alloy electrodes have been investigated in detail. XRD results showed that the as-deposited Fe–Sb–P alloy electrode exhibits an amorphous nature. Electrochemical tests indicated that at the 50th cycle, the Fe–Sb–P amorphous alloy electrodes can deliver a discharge capacity of 448 mAh g−1. The porous and amorphous structure of electrode of Fe–Sb–P alloy was beneficial in relaxing the volume expansion during cycling, which improved the cycle ability of Fe–Sb–P alloy electrode.

Three-dimensional (3D) porous materials of Sn–Ni alloy with reticular structure were prepared by electroplating using copper foam as current collector. The structure and electrochemical performance of the electroplated 3D porous Sn–Ni alloys were investigated in detail. Experimental results illustrated that the 3D porous Sn–Ni alloy consists of mainly Ni3Sn4 phase with a hexagonal structure. Galvonostatic charging/discharging of annealed 3D porous Sn–Ni alloy confirmed its excellent performances: at 50th charge–discharge cycle, the discharge specific capacity is 505 mAh g−1 and the corresponding charge (delithiation) specific capacity is 501 mAh g−1, yielding columbic efficiency as high as 99%. It has revealed that the porous structure of the alloy can restrain the pulverization of electrode in charge/discharge cycles, and accommodate partly the volume expansion and phase transition, resulting in a significant improvement of cycle life of the Sn–Ni electrode.

This paper reports the facile synthesis of a unique interleaved expanded graphite-embedded sulphur nanocomposite (S-EG) by melt-diffusion strategy. The SEM images of the S-EG materials indicate the nanocomposites consist of nanosheets with a layer-by-layer structure. Electrochemical tests reveal that the nanocomposite with a sulphur content of 60% (0.6S-EG) can deliver the highest discharge capacity of 1210.4 mAh g−1 at a charge–discharge rate of 280 mA g−1 in the first cycle, the discharge capacity of the 0.6S-EG remains as high as 957.9 mAh g−1 after 50 cycles of charge–discharge. Furthermore, at a much higher charge–discharge rate of 28 A g−1, the 0.6S-EG cathode can still deliver a high reversible capacity of 337.5 mAh g−1. The high sulphur utilization, excellent rate capability and reduced over-discharge phenomenon of the 0.6S-EG material are exclusively attributed to the particular microstructure and composition of the cathode.

Nanostructured Cu2Sb @C material was prepared through a simple polyol approach. Hollow Cu2Sb@C core–shell nanoparticles were obtained by controlling the amount of CuCl2 and time of replacement reaction. The hollow Cu2Sb@C nanoparticle electrode showed excellent cycling performance.

The formation of a spinel cubic framework is identified as a main trigger for the decreasing of the voltage profile for the high-voltage Li-rich manganese-based layered oxide, known as “voltage fade”. This dropping of the operating potential could cause massive loss in the energy density in lithium ion battery systems. To apply a profound understanding into the formation of a spinel cubic phase in Li1.2Ni0.12Co0.15Mn0.53O2 oxide, high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and galvanostatic intermittent titration technique (GITT) are employed. At different states of the initial electrochemical charge process, we found that the spinel cubic region mostly appears in the crystal defective area. The proportion of the spinel phase corresponds well to the Williamson–Hall type microstress value. At 4.70 V charged state, the Inverse Fast Fourier Transform (IFFT) graph shows structural transformation from an O3-type rhombohedral phase to a spinel cubic framework forced by stressful squeezing. The variations in occupation of lithium and manganese ions in the tetrahedral sites (Litetra and Mntetra), and the kinetic performances indicate two forms in the O3-spinel transition: “Li–Mn dumbbell” and spinel nucleus. These experimental results clarify the correlation between the formation of a spinel phase and microstress in Li-rich layered oxides and provide a possible way to depress voltage fade through compromising the crystal defects of the layered oxide.

The nanostructured mixture of a Sn2Fe and Sn2Co alloy composite with uniform cubic shaped particles has been synthesized by a reduction-thermal diffusion alloying reaction. The textural properties of the as-prepared samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. Compared with the Sn2Fe alloy, the alloy composite exhibits better reversibility and cycle performance. At a charge/discharge current density of 50 mA g−1, a reversible capacity of 510 mA h g−1 can be maintained after 50 cycles, and its capacity in the 50th cycle was retained at ca. 85% of that in the second cycle. When the current density is increased to 1000 mA g−1, a reversible capacity of 443 mA h g−1 can be still obtained. The ab initio simulation results indicate that Sn2Fe and Sn2Co have similar crystal structures, demonstrating that the two kinds of alloys can be mixed uniformly by the thermal diffusion alloying reaction. The superior electrochemical performance can be attributed to the homogeneously dispersed inactive metallic material (Fe and Co) nanostructure, which partly accommodates the volume change and also retains the integrity of the active material and matrix, resulting in good cycle performance of the composite electrode.