Porous Li4Ti5O12 anode material synthesized by one-step solid state method for electrochemical properties enhancement

A porous Li₄Ti₅O₁₂ anode material was successfully synthesized from mixture of LiCl and TiCl₄ with 70 wt% oxalic acid by a modified one-step solid state method. The anode material Li₄Ti₅O₁₂ exhibited a cubic spinel structure and only one voltage plateau occurred around 1.5 V. The initial capacity of porous Li₄Ti₅O₁₂ was 167 and 133 mAh g⁻¹ at 0.5 and 1C charge/discharge rate, respectively, and the capacity retention maintained above 98% after 200 cycles. The porous Li₄Ti₅O₁₂ structure showed promising rate performance with a capacity of 70 mAh g⁻¹ at charge/discharge 10C rate after 200 cycles. It was demonstrated that the porous structure could withstand 50C charge/discharge rate and exhibited excellent cycling stability.     

Synthesis and electrochemical properties of porous LiV3O8 as cathode materials for lithium-ion batteries

In this paper, we report on the synthesis of porous LiV₃O₈ by using a tartaric acid-assisted sol-gel process and their enhanced electrochemical properties for reversible lithium storage. The crystal structure, morphology and pore texture of the as-synthesized samples are characterized by means of XRD, SEM, TEM/HRTEM and N₂ adsorption/desorption measurements. The results show that the tartaric acid plays a pore-making function and the calcination temperature is an important influential factor to the pore texture. In particular, the porous LiV₃O₈ calcined at 300 °C (LiV₃O₈-300) exhibits hierarchical porous structure with high surface area of 152.4 m² g⁻¹. The electrochemical performance of the as-prepared porous LiV₃O₈ as cathode materials for lithium ion batteries is investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The porous LiV₃O₈-300 displays a maximum discharge capacity of 320 mAh g⁻¹ and remains 96.3% of its initial discharge capacity after 50 charge/discharge cycles at the current density of 40 mA g⁻¹ due to the enhanced charge transfer kinetics with a low apparent activity energy of 35.2 kJ mol⁻¹, suggesting its promising application as the cathode material of Li-ion batteries.     

Synthesis and characterization of in situ carbon-coated Li2FeSiO4 cathode materials for lithium ion battery

Li₂FeSiO₄/C composites with in situ carbon coating were synthesized via sol-gel method based on acid-catalyzed hydrolysis/condensation of tetraethoxysilane (TEOS) with sucrose and l-ascorbic acid as carbon additives, respectively. As-obtained Li₂FeSiO₄/C composites prepared with l-ascorbic acid as a carbon additive are composed of nanoparticulate Li₂FeSiO₄ in an intimate contact with a continuous thin layer of residual carbon and exhibit large specific surface area up to 395.7 m² g⁻¹. The results indicate that structure of the residual carbon is graphene-rich with obviously lower disordered/graphene (D/G) ratio. These as-obtained Li₂FeSiO₄/C composites exhibit first discharge capacity of 135.3 mAh g⁻¹ at C/16 and perform cycling stability, which are superior to those of Li₂FeSiO₄/C composites synthesized with sucrose as a carbon additive.     

Electrochemical lithium storage performance of ternary Zn-Co-Ni alloy thin film as negative electrodes by electrodeposition method

Ternary Zn-Co-Ni alloy film electrode as an anode has been investigated, for the first time, for the purpose of electrochemical lithium storage in lithium-ion batteries. In this study, the ternary Zn-Co-Ni alloy film electrode is prepared by electroplating method. The electrodes were examined using X-ray diffraction (XRD), FE-SEM with EDX, and impedance studies. The electrochemical results demonstrate that the Zn-Co-Ni alloy film electrode delivers an initial discharge capacity of 281 mAh g⁻¹ and improves to 650 mAh g⁻¹ at the end of 30th cycling with no capacity fading at 0.1 C rate. The charge-discharge properties of the Zn-Co-Ni alloy film electrode are as follows: insertion capacity of 650 mAh g⁻¹ and delithiation capacity of 512 mAh g⁻¹ in the 30th cycling, coulombic efficiency of about 80.0% and good cycling behavior. The results suggest that the ternary Zn-Co-Ni alloy thin film electrode obtained via electroplating shows a good candidate anode material for lithium-ion batteries.     

Fabrication and electrochemical behavior of flower-like ZnO-CoO-C nanowall arrays as anodes for lithium-ion batteries

This study reported the electrochemical performance of flower-like ZnO-CoO-C nanowall arrays as anodes of lithium-ion batteries. The arrays were fabricated through solution-immersion steps and subsequent calcination at 400 °C. At a rate of 0.5 C, the arrays exhibited a delithiation capacity of 438 mA h g⁻¹ at the 50th cycle. The arrays still delivered a reversible capacity of 224 mA h g⁻¹ at 2.0 C rate, much higher than those of the flower-like ZnO and ZnO-C nanowall arrays. The mechanism for the high capacity of flower-like ZnO-CoO-C nanowall arrays mainly resulted from the catalytic effect of Co phase on the decomposition of Li₂O and the conducting carbon layer formed on ZnO nanowalls. The present finding also provides a kind of nanostructured films that might be applied in solar cells and sensors, etc.     

A precursor route to synthesize mesoporous γ-MnO2 microcrystals and their applications in lithium battery and water treatment

MnCO₃ microstructures, including 2.3 μm microplates with the thickness of 200 nm and 3.1 μm microspheres stacked with 50 nm-thick sheets, were hydrothermally prepared in the assistance of sodium dodecyl benzene sulphonate (SDBS) and dodecyl sulfonic acid sodium (SDS), respectively. With the as-synthesized MnCO₃ as precursors followed by annealing at 400 °C for 4 h, mesoporous γ-MnO₂ microplates and microspheres with the pore size of 4-50 nm, which basically preserved the initial shapes, were obtained. The Brunauer-Emmett-Teller surface areas of the as-prepared γ-MnO₂ microplates and microspheres were 52.1 m² g⁻¹ and 50.2 m² g⁻¹, respectively. The electrochemical property tests over Li⁺ batteries showed that the initial discharge capacity of γ-MnO₂ microplates and microspheres were 1997 mAh g⁻¹ and 1533 mAh g⁻¹. Noticeably, even after 100 cycles, the discharge capacity of γ-MnO₂ microplates was still as high as 626 mAh g⁻¹, indicating the decent cycle behavior. In addition, mesoporous γ-MnO₂ was also applied as adsorbents in water treatment, and γ-MnO₂ microplates and microspheres could remove about 55% and 80% of Congo red.     

Structural and electrochemical hydrogen storage properties of Mg2Ni-based alloys

Four different methods, i.e. hydriding combustion synthesis + mechanical milling (HCS + MM), induction melting (followed by hydriding) + mechanical milling (IM(Hyd) + MM), combustion synthesis + mechanical milling (CS + MM) and induction melting + mechanical milling (IM + MM), were used to prepare Mg₂Ni-based hydrogen storage alloys used as the negative electrode material in a nickel-metal hydride (Ni/MH) battery. The structural and electrochemical hydrogen storage properties of the Mg₂Ni-based alloys have been investigated systematically. The XRD results indicate that the as-milled products show nanocrystalline or amorphous-like structures. Electrochemical measurements show that the as-milled hydrides exhibit higher discharge capacity and better electrochemical kinetic property than the as-milled alloys. Among the four different methods, the HCS + MM product possesses the highest discharge capacity (578 mAh g⁻¹), the best high rate dischargeability (HRD) and the highest exchange current density (58.8 mA g⁻¹). It is suggested that the novel method of HCS + MM is promising to prepare Mg-based hydrogen storage electrode alloy with high discharge capacity and activity.     

Synthesis of in situ network-like vapor-grown carbon fiber improved LiFePO4 cathode materials by microwave pyrolysis chemical vapor deposition

The low electronic conductivity of LiFePO₄ currently limits its use in lithium ion batteries. In order to solve the problem, in situ network-like vapor-grown carbon fiber (VGCF) improved LiFePO₄ cathode materials have been prepared in one step by microwave pyrolysis chemical vapor deposition. The phase, microstructure and electrochemical performances of the composites were investigated. Compared with the cathodes without in situ VGCF, the initial discharge capacity of the composite electrode increases from 84 mAh g⁻¹ to 123 mAh g⁻¹ at 3.0 C rate, and the charge transfer resistance varies from 420 Ω to 75 Ω. The possible reasons of those are proposed.     

Effect of the impurity LixNi1−xO on the electrochemical properties of 5 V cathode material LiNi0.5Mn1.5O4

The formation of impurity Li_xNi_1−xO when synthesizing spinel LiNi_0.5Mn_1.5O₄ using solid state reaction method, and its influence on the electrochemical properties of product LiNi_0.5Mn_1.5O₄ were studied. The secondary phase Li_xNi_1−xO emerges at high temperature due to oxygen deficiency for LiNi_0.5Mn_1.5O₄ and partial reduction of Mn⁴⁺ to Mn³⁺ in LiNi_0.5Mn_1.5O₄. Annealing process can diminish oxygen deficiency and inhibit impurity Li_xNi_1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi_0.5Mn_1.5O₄ that contains Li_xNi_1−xO can deliver about 120 mAh g⁻¹.     

Enhanced electrochemical performances of multi-walled carbon nanotubes modified Li3V2(PO4)3/C cathode material for lithium-ion batteries

The multi-walled carbon nanotubes (MWCNTs) modified Li₃V₂(PO₄)₃/C composite is synthesized by polyvinyl alcohol (PVA) based carbon-thermal reduction method using MWCNTs as a highly conductive agent. PVA mainly supplies a reductive atmosphere to reduce V⁵⁺ and provides a network of carbon to inhibit the aggregation of Li₃V₂(PO₄)₃ particles. The amorphous carbon coating and MWCNTs co-modified composite shows excellent high-rate lithium intercalation/deintercalation property and cycling performance between 3.0 and 4.3 V. The discharge capacities of 131.7 and 122.9 mAh g⁻¹ are obtained at rates of 1 C and 10 C, respectively, for the Li₃V₂(PO₄)₃/(C + MWCNTs). These improvements are attributed to the valid conducting networks of C + MWCNTs and the reduced Li₃V₂(PO₄)₃ particle size by the network carbon from the pyrolysis of PVA.     

Low temperature synthesis of Fe3O4 micro-spheres and its application in lithium ion battery

Fe₃O₄ micro-spheres with nanoparticles close-packed architectures were synthesized via a simple chemical method using (NH₄)₂Fe(SO₄)₂·6H₂O, hexamethylenetetramine, and NaF as reaction materials. This chemical synthesis took place in a vitreous jar under low temperature (90 °C) and atmospheric pressure. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ micro-spheres as anode electrode of lithium ion batteries were studied by conventional charge/discharge tests, which exhibit steady charge/discharge platforms at different current densities. The as-prepared Fe₃O₄ electrode shows high initial discharge capacity of 1166 and 1082 mAh g⁻¹ at current density of 0.05 and 0.1 mA cm⁻², respectively.     

Sol-gel synthesis and electrochemical performance of Li4Ti5O12/graphene composite anode for lithium-ion batteries

Li₄Ti₅O₁₂/graphene composite was prepared by a facile sol-gel method. The lattice structure and morphology of the composite were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The electrochemical performances of the electrodes have been investigated compared with the pristine Li₄Ti₅O₁₂ synthesized by a similar route. The Li₄Ti₅O₁₂/graphene composite presents a higher capacity and better cycling performance than Li₄Ti₅O₁₂ at the cutoff of 2.5-1.0 V, especially at high current rate. The excellent electrochemical performance of Li₄Ti₅O₁₂/graphene electrode could be attributed to the improvement of electronic conductivity from the graphene sheets. When discharged to 0 V, the Li₄Ti₅O₁₂/graphene composite exhibited a quite high capacity over 274 mAh g⁻¹ below 1.0 V, which was quite beneficial for not only the high energy density but also the safety characteristic of lithium-ion batteries.     

Fabrication of highly ordered porous nickel phosphide film and its electrochemical performances toward lithium storage

Highly ordered porous Ni₃P film was successfully electrodeposited through a self-assembled monodisperse polystyrene sphere template on copper substrate after heat treatment. The spherical pores left in the film after the removal of polystyrene spheres are well-ordered and close-packed. The diameter of the pores arranged in the film is about 800 nm and the thickness of the wall connecting adjacent pores is 60 nm. As anode for lithium ion batteries, the nanostructured porous Ni₃P film exhibits improved capability and reversibility over the dense one. After 50 cycles, the reversible capacity of the porous Ni₃P film is 403 mAh g⁻¹ and 239 mAh g⁻¹ at 0.2 C and 2 C, maintaining 78.1% and 67.9% of the capacity in the 2nd cycle, respectively. The enhanced electrochemical performance of the porous film is attributed to the better contact between Ni₃P and electrolyte, which provides more sites for Li⁺ accommodation, shortens the diffusion length of Li⁺ and enhances the kinetics of electrode process. Moreover, the porous structure is stable and can sustain well even after 50 cycles.     

A literature review and test: Structure and physicochemical properties of spinel LiMn2O4 synthesized by different temperatures for lithium ion battery

A series of LiMn₂O₄ spinel was prepared by adipic acid-assisted sol–gel method at different temperatures. The structure and physicochemical properties of spinel LiMn₂O₄ synthesized by different temperatures were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron micrographs (SEM), inductively coupled plasma-mass spectroscopy (ICP-MS), galvanostatic charge–discharge test, and cyclic voltammetry (CV), respectively. TG–DTA shows that the weight loss occurs in four temperature regions during the synthesis of LiMn₂O₄. XRD indicates that the sintering temperature affects the formation of spinel phase, and prominent LiMn₂O₄ spinel powder with smaller atom location confusion forms about 800 °C. XPS reveals that the manganese oxidation state in spinel lithium manganese oxide synthesized at different temperatures is between +3 and +4. SEM shows that LiMn₂O₄ spinel synthesized at 800 °C has the uniform, nearly cubic structure morphology with narrow size distribution. ICP-MS indicates that the average chemical valence of Mn element of LiMn₂O₄ synthesized at 800 °C is the most close to 3.5 among the samples synthesized at different temperatures. CV illustrates that the LiMn₂O₄ synthesized at 800 °C has the best electrochemical activity. Charge–discharge test explains that the capacity retention sintered at 350, 700 and 800 °C over the first 50 cycles is 93.6%, 86.1% and 85.2%, respectively, but the discharge capacity at the 50th cycle is 82.2, 104.8 and 110.8 mAh g⁻¹, respectively.     

Synthesis and electrochemical performance of Li(Ni0.8Co0.15Al0.05)0.8(Ni0.5Mn0.5)0.2O2 with core-shell structure as cathode material for Li-ion batteries

The core-shell structure cathode material Li(Ni_0.8Co_0.15Al_0.05)_0.8(Ni_0.5Mn_0.5)_0.2O₂ (LNCANMO) was synthesized via a co-precipitation method. Its applicability as a cathode material for lithium ion batteries was investigated. The core-shell particle consists of LiNi_0.8Co_0.15Al_0.05O₂ (LNCAO) as the core and a LiNi_0.5Mn_0.5O₂ as the shell. The thickness of the LiNi_0.5Mn_0.5O₂ layer is approximately 1.25 μm, as estimated by field emission scanning electron microscopy (FE-SEM). The cycling behavior between 2.8 and 4.3 V at a current rate of 18 mA g⁻¹ shows a reversible capacity of about 195 mAh g⁻¹ with little capacity loss after 50 cycles. High-rate capability testing shows that even at a rate of 5 C, a stable capacity of approximately 127 mAh g⁻¹ is retained. In contrast, the capacity of LNCAO rapidly decreases in cyclic and high rate tests. The observed higher current rate capability and cycle stability of LNCANMO can be attributed to the lower impedance including charge transfer resistance and surface film resistance. Differential scanning calorimetry (DSC) indicates that LNCANMO had a much improved oxygen evolution onset temperature of approximately 251 °C, and a much lower level of exothermic-heat release compared to LNCAO. The improved thermal stability of the LNCANMO can be ascribed to the thermally stable outer shell of LiNi_0.5Mn_0.5O₂, which suppresses oxygen release from the host lattice and not directly come into contact with the electrolyte solution. In particular, LNCANMO is shown to exhibit improved electrochemical performance and is a safe material for use as an electrode for lithium ion batteries.     

Large-scale synthesis of macroporous SnO2 with/without carbon and their application as anode materials for lithium-ion batteries

The macroporous SnO₂ is prepared using close packed carbonaceous sphere template which synthesized from glucose by hydrothermal method. The structure and morphology of the macroporous SnO₂ are evaluated by XRD and FE-SEM. The average pore size of the macroporous SnO₂ is about 190 nm and its wall thickness is less than 10 nm. When the macroporous SnO₂ filled with carbon is used as an anode material for lithium-ion battery, the capacity is about 380 mAh g⁻¹ after 70 cycles. The improved cyclability is attributed to the carbon matrix which is used as an effective physical buffer to prevent the collapse of the well dispersed macroporous SnO₂.     

Synthesis and rate performance of lithium vanadium phosphate as cathode material for Li-ion batteries

A sphere-like carbon-coated Li₃V₂(PO₄)₃ composite was synthesized by carbothermal reduction method with two sessions of ball milling followed by spray-drying with the dispersant of polyethylene glycol added. The structure, particle size, and surface morphology of the cathode material were investigated via X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. Results indicate that the Li₃V₂(PO₄)₃/C composite has a sphere-like morphology composed of a large number of carbon-coated ultrafine particles linked together with a monoclinic structure. In the voltage range of 3.0-4.3 V, it exhibits the discharge capacities of 130 mAh g⁻¹ and 100 mAh g⁻¹ at 0.2 C and 20 C rates, respectively. This behavior indicates that the obtained Li₃V₂(PO₄)₃/C material has excellent rate capability.     

Preparation of Fe2O3/graphene composite and its electrochemical performance as an anode material for lithium ion batteries

The micro-sized sphere Fe₂O₃ particles doped with graphene nanosheets were prepared by a facile hydrothermal method. The obtained Fe₂O₃/graphene composite as the anode material for lithium ion batteries showed a high discharge capacity of 660 mAh g⁻¹ during up to 100 cycles at the current density of 160 mA g⁻¹ and good rate capability. The excellent electrochemical performance of the composite can be attributed to that graphene served as dispersing medium to prevent Fe₂O₃ microparticles from agglomeration and provide an excellent electronic conduction pathway.     

Investigation on 3-dimensional carbon foams/LiFePO4 composites as function of the annealing time under inert atmosphere

The morphological and electrochemical investigation of 3-dimensional (3D) carbon foams coated with olivine structured lithium iron phosphate as function of the annealing time under nitrogen atmosphere is reported. The LiFePO₄ as cathode material for lithium ion batteries was prepared by a Pechini-assisted sol-gel process. The coating has been successfully performed on commercially available 3D-carbon foams by soaking in aqueous solution containing lithium, iron salts and phosphates at 70 °C for 2-4 h. After drying-out, the composites were annealed at 600 °C for different times ranging from 0.4 to 10 h under nitrogen. The formation of the olivine-like structured LiFePO₄ was confirmed by X-ray diffraction analysis performed on the powder prepared under similar conditions. The surface investigation of the prepared composites showed the formation of a homogeneous coating by LiFePO₄ on the foams. The cyclic voltammetry curves of the composites show an enhancement of electrode reaction reversibility by increasing the annealing time. The electrochemical measurements on the composites showed good performances delivering a discharge specific capacity of 85 mAh g⁻¹ at a discharging rate of C/25 at room temperature after annealing for 0.4 h and 105 mAh g⁻¹ after annealing for 5 h.     

LiFePO4/C composite cathode material with a continuous porous carbon network for high power lithium-ion battery

A series of LiFePO₄/porous carbon composites with different LiFePO₄ loading amounts were prepared by impregnation from ethanol solution of the LiFePO₄ precursors. The samples were characterized using X-ray powder diffraction (XRD), thermogravimetry (TG), differential scanning calorimetric (DSC), transmission electron microscopy (TEM) and nitrogen sorption prior to the electrochemical testing. The size and morphology of the porous carbon supported LiFePO₄ nanoparticles depended strongly on the LiFePO₄ loading amounts. The impact of LiFePO₄ loading on the electrochemical performance of the composites was discussed in detail. Among all the samples, the LiFePO₄/microporous carbon composites with the LiFePO₄ loading amount of 19.10 wt.% and 35.58 wt.%, respectively, demonstrated high rate performance with discharge capacity of 60 mAh g⁻¹ and 66 mAh g⁻¹ at 50 C.