Hydrothermal synthesis of Co2SnO4 nanocrystals as anode materials for Li-ion batteries

Cubic spinel Co₂SnO₄ nanocrystals are successfully synthesized via a simple hydrothermal reaction in alkaline solution. The effect of alkaline concentration, hydrothermal temperature, and hydrothermal time on the structure and morphology of the resultant products were investigated based on X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is demonstrated that pure Co₂SnO₄ nanocrystals with good crystallinity can be obtained in NaOH solution (2.0 M) at 240 °C for 48 h. The galvanostatic charge/discharge and cyclic voltammetry were conducted to measure the electrochemical performance of the Co₂SnO₄ nanocrystals. It is shown that Co₂SnO₄ nanocrystals exhibit good electrochemical activity with high reversible capacity (charge capacity) of 1088.8 mAh g⁻¹ and good capacity retention as anode materials for Li-ion batteries, much better than that of bulk Co₂SnO₄ prepared by high temperature solid-state reaction.     

Preparation and electrochemical properties of TiO2 hollow spheres as an anode material for lithium-ion batteries

TiO₂ hollow spheres are fabricated by a sol-gel process using carbon spheres as template. The diameter and the shell thickness of the TiO₂ hollow spheres are about 400-600 nm and 60-80 nm, respectively. The electrochemical properties of the hollow spheres are investigated by galvanostatic cycling and cyclic voltammetry (CV) measurements. The initial discharge capacity reaches 291.2 mAh g⁻¹ at a current density of 60 mA g⁻¹. The average discharge capacity loss is about 1.72 mAh g⁻¹ per cycle from the 2nd to the 40th cycles and the coulombic efficiency is approximately 98% after 40 cycles, indicating excellent cycling stability and reversibility.     

Dual active material composite cathode structures for Li-ion batteries

The efficacy of composite Li-ion battery cathodes made by mixing active materials that possessed either high-rate capability or high specific energy was examined. The cathode structures studied contained carbon-coated LiFePO₄ and either Li[Li_0.17Mn_0.58Ni_0.25]O₂ or LiCoO₂. These active materials were arranged using three different electrode geometries: fully intermixed, fully separated, or layered. Discharge rate studies, cycle-life evaluation, and electrochemical impedance spectroscopy studies were conducted using coin cell test structures containing Li-metal anodes. Results indicated that electrode configuration was correlated to rate capability and degree of polarization if there was a large differential between the rate capabilities of the two active material species.     

Carbon particles modified macroporous Si/Ni composite as an advanced anode material for lithium ion batteries

Carbon particles modified macroporous Si/Ni composite (MP-Si/Ni/C) is easily obtained via a facile fabrication of porous Si/Ni precursor by dealloying SiNiAl alloy followed by a surface growth of carbon nanoparticles. MP-Si/Ni/C composite possesses the multiply conductivity modification that are built through mixing Ni dispersoid and growing one layer of carbon particles. Coupled with the structural advantages of interconnected network backbone, rich voids, and the coated carbon particles, MP-Si/Ni/C exhibits dramatically enhanced lithium storage performances with excellent reversible capacity, enhanced rate performance, as well as outstanding cycling stability compared with pure MP-Si and MP-Si/Ni. Especially, the reversible capacity remains up to 1113.1 and 708.8 mA h g⁻¹ at the current densities of 200 and 1000 mA g⁻¹ after 120 cycles, respectively. Besides, it shows excellent rate capability even when continuously cycled at high current density of 3000 mA g⁻¹. With the advantages of unique structure, excellent performances, and facile preparation, the as-made MP-Si/Ni/C composite shows promising application potential as an alternative anode for lithium ion batteries.     

A novel CuO-nanotube/SnO2 composite as the anode material for lithium ion batteries

A novel CuO-nanotubes/SnO₂ composite was prepared by a facile solution method and its electrochemical properties were investigated as the anode material for Li-ion battery. The as-prepared composite consisted of monoclinic-phase CuO-nanotubes and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were dramatically decorated on the CuO-nanotubes. The composite showed higher reversible capacity, better durability and high rate performance than the pure SnO₂. The better electrochemical performance could be attributed to the introducing of the CuO-nanotubes. It was found that the CuO-nanotubes were reduced to metallic Cu in the first discharge cycle, which can retain tube structure of the CuO-nanotubes as a tube buffer to alleviate the volume expansion of SnO₂ during cycling and act as a good conductor to improve the electrical conductivity of the electrodes.     

A three-dimensional macroporous Cu/SnO2 composite anode sheet prepared via a novel method

A three-dimensional macroporous Cu/SnO₂ composite anode sheet for lithium ion batteries was prepared via a novel method that is based on selective reduction of metal oxides at appropriate temperatures. SnO₂ particles were imbedded on the Cu particles within the three-dimensionally interconnected Cu substrate, and the whole composite sheet was used directly as an electrode without adding extra conductive carbons and binders. Compared with the SnO₂-based electrode prepared via the conventional tape-casting method on Cu foil, the porous Cu/SnO₂ composite electrode shows significantly improved battery performance. This methodology produces limited wastes and is also adaptable to many other materials. It is a promising approach to make macroporous electrode for Li-ion batteries.     

Comparison between microparticles and nanostructured particles of FeSn2 as anode materials for Li-ion batteries

The performances and mechanisms of two types of anodes formed by FeSn₂ microparticles and nanostructured FeSn₂, respectively, were studied by Mössbauer spectroscopy and electrochemical testing. The specific capacity, which is within the range 400-600 mAh g⁻¹ even at high C-rate, did not vary with cycle number over 50-60 cycles for the microparticles but progressively decreased for the nanostructured material. In the two cases, the first discharge consists in the irreversible transformation of FeSn₂ into Fe/Li₇Sn₂ nanocomposite. The capacity fade is attributed to the growth and/or coalescence of the particles during cycling.     

SiOx-graphite as negative for high energy Li-ion batteries

Negative electrodes containing SiO_x were investigated as alternative negative electrodes to carbon for Li-ion batteries. The results obtained on the effect of binders and carbon additives on the electrochemical performance (i.e., reversible capacity, coulombic efficiency, charge-discharge rate capability) of the SiO_x-graphite electrode and SiO_x electrode are presented. SEM analysis that utilizes facilities for in situ and ex situ studies were applied to better understand the performance and cycle life of the SiO_x-based electrodes. The SEM analysis clearly showed that the SiO_x particles expand and contract during charge-discharge cycling, and that some of the particles undergo mechanical degradation during this process. The SiO_x-graphite electrode with polyimide binder exhibited a stable capacity of 600 mAh g⁻¹ during high-rate charge-discharge from C/4 to 1C. These results suggest that the use of a flexible binder like polyimide and reasonably small SiO_x particles (nano-particles) facilitates improved cycle life and higher rate capability.     

Synthesis and characterization of Nd doped LiMn2O4 cathode for Li-ion rechargeable batteries

Spinel powders of LiMn_1.99Nd_0.01O₄ have been synthesized by chemical synthesis route to prepare cathodes for Li-ion coin cells. The structural and electrochemical properties of these cathodes were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, and charge-discharge studies. The cyclic voltammetry of the cathodes revealed the reversible nature of Li-ion intercalation and deintercalation in the electrochemical cell. The charge-discharge characteristics for LiMn_1.99Nd_0.01O₄ cathode materials were obtained in 3.4–4.3 V voltage range and the initial discharge capacity of this material were found to be about 149 mAh g⁻¹. The coin cells were tested for up to 25 charge-discharge cycles. The results show that by doping with small concentration of rare-earth element Nd, the capacity fading is considerably reduced as compared to the pure LiMn₂O₄ cathodes, making it suitable for Li-ion battery applications.     

Lithium recycling behaviour of nano-phase-CuCo2O4 as anode for lithium-ion batteries

Nano-CuCo₂O₄ is synthesized by the low-temperature (400 °C) and cost-effective urea combustion method. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) studies establish that the compound possesses a spinel structure and nano-particle morphology (particle size (10–20 nm)). A slight amount of CuO is found as an impurity. Galvanostatic cycling of CuCo₂O₄ at 60 mA g⁻¹ in the voltage range 0.005–3.0 V versus Li metal exhibits reversible cycling performance between 2 and 50 cycles with a small capacity fading of 2 mAh g⁻¹ per cycle. Good rate capability is also found in the range 0.04–0.94C. Typical discharge and charge capacity values at the 20th cycle are 755(±10) mAh g⁻¹ (∼6.9 mol of Li per mole of CuCo₂O₄) and 745(±10) mAh g⁻¹ (∼6.8 mol of Li), respectively at a current of 60 mA g⁻¹. The average discharge and charge potentials are ∼1.2 and ∼2.1 V, respectively. The underlying reaction mechanism is the redox reaction: Co ↔ CoO ↔ Co₃O₄ and Cu ↔ CuO aided by Li₂O, after initial reaction with Li. The galvanostatic cycling studies are complemented by cyclic voltammetry (CV), ex situ TEM and SAED. The Li-cycling behaviour of nano-CuCo₂O₄ compares well with that of iso-structural nano-Co₃O₄ as reported in the literature.     

LiBF3Cl as an alternative salt for the electrolyte of Li-ion batteries

LiBF₃Cl was synthesized by reacting BF₃ etherate and LiCl in an organic media, and evaluated as a salt for the electrolyte of Li-ion batteries. XRD results showed that LiBF₃Cl has the same crystallographic structure as LiBF₄ except for little difference in the lattice parameter. With a 3:7 (w/w) solvent blend of ethylene carbonate and ethyl methyl carbonate, LiBF₃Cl electrolyte was found to have lower liquidus temperature than LiBF₄ analogue either due to its higher solubility or due to its higher tendency in forming a super-cooling solution, which was related to the less symmetry of BF₃Cl⁻ anion. Meanwhile, LiBF₃Cl electrolyte displayed excellent ability in passivating Al at high potentials due to the similar chemical composition of LiBF₃Cl and LiBF₄. Most importantly, the LiBF₃Cl electrolyte was superior to the LiBF₄ electrolyte in facilitating the formation of solid electrolyte interphase (SEI) on graphite electrode, which not only increased Coulombic efficiencies of the SEI formation, but also prolonged cycle life of the Li-ion batteries. The merits above make LiBF₃Cl very promising as an alternative lithium salt for the electrolyte of Li-ion batteries.     

A high performance silicon/carbon composite anode with carbon nanofiber for lithium-ion batteries

The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with carbon nanofiber (CNF) was examined as an anode for lithium-ion batteries. CNF was incorporated into the composite by two methods; direct mixing of CNF with the nano-Si powder coated with carbon produced by pyrolysis of PVC (referred to as Si/C/CNF-1) and mixing of CNF, nano-Si powder, and PVC with subsequent firing (referred to as Si/C/CNF-2). The external Brunauer-Emmett-Teller (BET) surface area of Si/C/CNF-1 was comparable to that of Si/C/CNF-2. The micropore BET surface area of Si/C/CNF-2 (73.86 m² g⁻¹) was extremely higher than that of Si/C/CNF-1 (0.74 m² g⁻¹). The composites prepared by both methods exhibited high capacity and excellent cycling stability for lithium insertion and extraction. A capacity of more than 900 mA h g⁻¹ was maintained after 30 cycles. The coulombic efficiency of the first cycle for Si/C/CNF-1 was as low as 53%, compared with 73% for Si/C/CNF-2. Impedance analysis of cells containing these anode materials suggested that the charge transfer resistance for Si/C/CNF-1 was not changed by cycling, but that Si/C/CNF-2 had high charge transfer resistance after cycling. A composite electrode prepared by mixing Si/C/CNF-2 and CNF exhibited a high reversible capacity at high rate, excellent cycling performance, and a high coulombic efficiency during the first lithium insertion and extraction cycles.     

Polymer-derived-SiCN ceramic/graphite composite as anode material with enhanced rate capability for lithium ion batteries

We report on a new composite material in view of its application as a negative electrode in lithium-ion batteries. A commercial preceramic polysilazane mixed with graphite in 1:1 weight ratio was transformed into a SiCN/graphite composite material through a pyrolytic polymer-to-ceramic conversion at three different temperatures, namely 950 °C, 1100 °C and 1300 °C. By means of Raman spectroscopy we found successive ordering of carbon clusters into nano-crystalline graphitic regions with increasing pyrolysis temperature. The reversible capacity of about 350 mAh g⁻¹ was measured with constant current charging/discharging for the composite prepared at 1300 °C. For comparison pure graphite and pure polysilazane-derived SiCN ceramic were examined as reference materials. During fast charging and discharging the composite material demonstrates enhanced capacity and stability. Charging and discharging in half an hour lead to about 200 and 10 mAh g⁻¹, for the composite annealed at 1300 °C and pure graphite, respectively. A clear dependence between the final material capacity and pyrolysis temperature is found and discussed with respect to possible application in batteries, i.e. practical discharging potential limit. The best results in terms of capacity recovered under 1 V and high rate capability were also obtained for samples synthesized at 1300 °C.     

Constructing Janus SnSSe and graphene heterostructures as promising anode materials for Li-ion batteries

Developing efficient anode materials for Li-ion batteries is becoming increasingly important but is still challenging to collect relevant information about their adsorption and diffusion. Herein, by means of density functional theory (DFT) computations, the Janus SnSSe, and graphene van der Waals heterostructures (ie, SSnSe/G and SeSnS/G) are systematically investigated by first principles calculations, aiming at constructing promising anode materials for Li-ion batteries (LIBs). The results have demonstrated that the SnSSe/G heterostructures exhibits a semimetal-to-metal transition after incorporating Li, indicating enhanced conductivity compared to monolayer Janus SnSSe or graphene. Moreover, the SnSSe/G heterostructures can maintain favorable structural stability and ultrahigh stiffness well after applying the strain or adsorption of lithium atoms, thereby ensuring the pulverization resistance. In addition, the energy barriers of Li atoms diffusion are very low, which are expected to achieve a fast charge/discharge rate. Meanwhile, the estimated storage capacity of Li on SnSSe/G heterostructures could achieve 472.66 mA h g^?1, which greatly improves the storage capacity. These interesting results show that Janus SnSSe/G heterostructures could be used as excellent anode materials for LIBs.     

Preparation and electrochemical properties of carbon-doped TiO2 nanotubes as an anode material for lithium-ion batteries

Carbon-doped TiO₂ nanotubes were synthesized through a sol–gel and subsequent hydrothermal process. Transmission electron microscopy and X-ray diffraction showed that the products are uniformly straight tubes with the diameter around 10 nm in anatase-type. The electrochemical performances of the nanotubes were tested by constant current discharge/charge, cyclic voltammetry, and electrochemical impedance spectroscopy. The initial discharge capacity reaches 291.7 mAh g⁻¹ with a coulombic efficiency of 91.7% at a current density of 70 mA g⁻¹. There is a distinct potential plateau near 1.75 and 1.89 V (versus Li⁺/Li) in the lithium intercalation and extraction processes, respectively, and the lithium insertion capacity is about 204 mAh g⁻¹ over the plateau of 1.75 V region in the first cycle. From the 2nd to the 30th cycles, the average reversible capacity loss is less than 1.73 mAh g⁻¹ per cycle. After 30 cycles, the reversible capacity still remains 211 mAh g⁻¹ with a coulombic efficiency larger than 99.7%, implying a perfect reversibility and cycling stability.     

Electrochemical properties of Li2ZrO3-coated silicon/graphite/carbon composite as anode material for lithium ion batteries

Silicon/graphite/disordered carbon (Si/G/DC) is coated by Li₂ZrO₃ using Zr(NO₃)₄·5H₂O and CH₃COOLi·2H₂O as coating reagents. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to characterize Li₂ZrO₃-coated Si/G/DC composite. The Li₂ZrO₃-coated Si/G/DC composite exhibits a high reversible capacity with no capacity fading from 2nd to 70th cycle, indicating its excellent cycleability when used as anode materials for lithium ion batteries. A compact and stable solid-electrolyte interphase (SEI) layer is formed on the surface of Li₂ZrO₃-coated Si/G/DC electrode. Analysis of electrochemical impedance spectra (EIS) shows that the resistance of the coated material exhibits less variation during cycling, which indicates the integrity of electrode structure is kept during cycling. XPS shows that F and P elements do not appear in the SEI layers of Li₂ZrO₃-coated Si/G/DC electrode, while they have a relatively high content in SEI layers of Si/G/DC electrode. The improvement of Li₂ZrO₃-coated Si/G/DC is attributed to the decrease of lithium insertion depth and the formation of stable SEI film.     

Application of SiO/C composite anode material for lithium -ion batteries

硅基材料因其较高的比容量而受到研究者广泛的关注。本文选取高比容量SiOx与NG复合材料作为锂离子电池负极材料,研究了不同SiO/C复合比例对全电池的能量密度和循环性能的影响。不同比例SiOx/C复合材料的首次容量和首次效率有明显差别。与石墨材料相比,SiOx/C复合材料的膨胀程度略有增加。随着SiOx比例的增加,全电池的能量密度先是上升然后下降,但其循环稳定性却有所降低。当SiOx比例在4%时,全电池能量密度提升1.2%,500周循环后容量保持率在80%以上,可以满足商业化锂离子电池的使用要求。     

Lithium-storage and cycleability of nano-CdSnO3 as an anode material for lithium-ion batteries

Nano-CdSnO₃ is prepared by thermal decomposition of the precursor, CdSn(OH)₆ at 600 °C for 6 h in air. The material is characterized physically by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and selected-area electron diffraction (SAED) techniques. Nano-CdSnO₃ exhibits a reversible and stable capacity of 475(±5) mAh g⁻¹ (∼5 mol of cycleable Li per mole of CdSnO₃) for at least 40 cycles between 0.005 and 1.0 V at a current rate of 0.13 C. Extensive capacity fading is found when cycling in the range 0.005-1.3 V. Cyclic voltammetry studies complement galvanostatic cycling data and reveal average discharge and charge potentials of 0.2 and 0.4 V, respectively. The proposed reaction mechanism is supported by ex situ XRD, TEM and SAED studies. The electrochemical impedance spectra taken during 1st and 10th cycle are fitted with an equivalent circuit to evaluate impedance parameters and the apparent chemical diffusion coefficient (DLi⁺) of Li. The bulk impedance, R_b, dominates at low voltages (≤0.25 V), whereas the combined surface film and charge-transfer impedance (R_(sf+ct)) and the Warburg impedance dominate at higher voltages, ≥0.25 V. The DLi⁺ is in the range of (0.5-0.9) × 10⁻¹³ cm² s⁻¹ at V = 0.5-1.0 V during the 10th cycle.     

Synthesis and characterization of electrochemically active graphite–silicon–tin composite anodes for Li-ion applications

Electrochemically active Si_0.66Sn_0.34 (SiSn) composite alloys dispersed in a carbon (graphite) matrix were synthesized using both wet and dry high-energy mechanical milling (HEMM). The resultant composites are comprised of amorphous carbon (in the case of dry HEMM) or crystalline carbon (in the case of wet HEMM), and crystalline silicon and tin (for both cases) as verified by X-ray diffraction (XRD). The XRD results also indicate the presence of iron–tin intermetallic (FeSn₂) arising as a contaminant during dry HEMM. The composite composition of 85C–15[Si_0.66Sn_0.34] (mol%) resulted in reversible discharge capacities as high as 800 mAh g⁻¹ with a reasonable capacity retention (1.36% loss/cycle). Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analyses were further conducted to examine the surface of the electrode and to determine the presence/absence of organic species resulting from reactions between the electrode, lithium ions and electrolyte, respectively.     

Synthesis and characterization of LiNi0.6Mn0.4−xCoxO2 as cathode materials for Li-ion batteries

LiNi_0.6Co_xMn_0.4−xO₂ (x = 0.05, 0.10, 0.15, 0.2) cathode materials are prepared, and their structural and electrochemical properties are investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetric (DSC) and charge–discharge test. The results show that well-ordering layered LiNi_0.6Co_xMn_0.4−xO₂ (x = 0.05, 0.10, 0.15, 0.2) cathode materials are successfully prepared in air at 850 °C. The increase of the Co content in LiNi_0.6Mn_0.4−xCo_xO₂ leads to the acceleration of the grain growth, the increase of the initial discharge capacity and the deterioration of the cycling performance of LiNi_0.6Mn_0.4−xCo_xO₂. It also leads to the enhancement of the ratio Ni³⁺/Ni²⁺ in LiNi_0.6Co_xMn_0.4−xO₂, which is approved by the XPS analysis, resulting in the increase of the phase transition during cycling. This is speculated to be main reason for the deteriotion of the cycling performance. All synthesized LiNi_0.6Co_xMn_0.4−xO₂ samples charged at 4.3 V show exothermic peaks with an onset temperature of larger than 255 °C, and give out less than 400 J g⁻¹ of total heat flow associated with the peaks in DSC analysis profile, exhibiting better thermal stability. LiNi_0.6Co_0.05Mn_0.35O₂ with low Co content and good thermal stability presents a capacity of 156.6 mAh g⁻¹ and 98.5% of initial capacity retention after 50 cycles, showing to be a promising cathode materials for Li-ion batteries.