Fabrication and electrochemical characterization of a vertical array of MnO2 nanowires grown on silicon substrates as a cathode material for lithium rechargeable batteries

A complementary metal-oxide-semiconductor (CMOS) compatible process for fabricating on-chip microbatteries based on nanostructures has been developed by growing manganese dioxide nanowires on silicon dioxide (SiO₂)/silicon (Si) substrate as a cathode material for lithium rechargeable batteries. High aspect-ratio anodized aluminum oxide (AAO) template integrated on SiO₂/Si substrates can be exploited for fabrication of a vertical array of nanowires having high surface area. The electrolytic manganese dioxide (EMD) nanowires are galvanostatically synthesized by direct current (dc) electrodeposition. The microstructure of these nanowire arrays is investigated by scanning electron microscopy and X-ray diffraction. Their electrochemical tests show that the discharge capacity of about 150 mAh g⁻¹ is maintained during a few cycles at the high discharge/charge rate of 300 mA g⁻¹.     

Electrochemical properties of LiFePO4 prepared via hydrothermal route

LiFePO₄ as a cathode material for rechargeable lithium batteries was prepared by hydrothermal process at 170 °C under inert atmosphere. The starting materials were LiOH, FeSO₄, and (NH₄)₂HPO₄. The particle size of the obtained LiFePO₄ was 0.5 μm. The electrochemical properties of LiFePO₄ were characterized in a mixed solvent of ethylene carbonate and diethyl carbonate (1:1 in volume) containing 1.0 mol dm⁻³ LiClO₄. The hydrothermally synthesized LiFePO₄ exhibited a discharge capacity of 130 mA h g⁻¹, which was smaller than theoretical capacity (170 mA h g⁻¹). The annealing of LiFePO₄ at 400 °C in argon atmosphere was effective in increasing the discharge capacity. The discharge capacity of the annealed LiFePO₄ was 150 mA h g⁻¹.     

Effects of roasting temperature and modification on properties of Li2FeSiO4/C cathode

Li₂FeSiO₄/C cathodes were synthesized by combination of wet-process method and solid-state reaction at high temperature, and effects of roasting temperature and modification on properties of the Li₂FeSiO₄/C cathode were investigated. The XRD patterns of the Li₂FeSiO₄/C samples indicate that all the samples are of good crystallinity, and a little Fe₃O₄ impurity was observed in them. The primary particle size rises as the roasting temperature increases from 600 to 750 °C. The Li₂FeSiO₄/C sample synthesized at 650 °C has good electrochemical performances with an initial discharge capacity of 144.9 mAh g⁻¹ and the discharge capacity remains 136.5 mAh g⁻¹ after 10 cycles. The performance of Li₂FeSiO₄/C cathode is further improved by modification of Ni substitution. The Li₂Fe_0.9Ni_0.1SiO₄/C composite cathode has an initial discharge capacity of 160.1 mAh g⁻¹, and the discharge capacity remains 153.9 mAh g⁻¹ after 10 cycles. The diffusion coefficient of lithium in Li₂FeSiO₄/C is 1.38 × 10⁻¹² cm² s⁻¹ while that in Li₂Fe_0.9Ni_0.1SiO₄/C reaches 3.34 × 10⁻¹² cm² s⁻¹.     

Cathode performance of olivine-type LiFePO4 synthesized by chemical lithiation

Chemical lithiation with LiI in acetonitrile was performed for amorphous FePO₄ synthesized from an equimolar aqueous suspension of iron powder and an aqueous solution of P₂O₅. An orthorhombic LiFePO₄ olivine structure was obtained by annealing a chemically lithiated sample at 550 °C for 5 h in Ar atmosphere. The average particle size remained at approximately 250 nm even after annealing. The lithium content in the sample was quantitatively confirmed by Li atomic absorption analysis and ⁵⁷Fe Mössbauer spectroscopy. While an amorphous FePO₄/carbon composite cathode has a monotonously decreasing charge–discharge profile with a reversible capacity of more than 140 mAh g⁻¹, the crystallized LiFePO₄/carbon composite shows a 3.4 V plateau corresponding to a two-phase reaction. This means that the lithium in the chemically lithiated sample is electrochemically active. Both amorphous FePO₄ and the chemically lithiated and annealed crystalline LiFePO₄ cathode materials showed good cyclability (more than 140 mAh g⁻¹ at the 40th cycle) and good discharge rate capability (more than 100 mAh g⁻¹ at 5.0 mA cm⁻²). In addition, the fast-charge performance was found to be comparable to that with LiCoO₂.     

Electrochemical performance of VOMoO4 as negative electrode material for Li ion batteries

Polycrystalline samples of VOMoO₄ are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005–3 V versus lithium. The reaction mechanism of a VOMoO₄ electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g⁻¹) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li₄MoO₅ during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g⁻¹ is obtained after 80 cycles when cycling is performed at a current density of 120 mA g⁻¹.     

Electrochemical behavior of Li3−xM′xV2−yM″y(PO4)3 (M′ = K, M″ = Sc, Mg + Ti)/C composite cathode material for lithium-ion batteries

Composites of monoclinic Li_3−xM′_xV_2−yM″_2y(PO₄)₃ (M′ = K, M″ = Sc, Mg + Ti) with carbon were synthesized by solid-state reaction using oxalic acid or 6% H₂/Ar gas mixture as reducing agents at sintering temperature of 850 °C. The samples were characterized by X-ray diffraction (XRD), voltammetry and electrochemical galvanostatic cycling. The capacity of Li₃V₂(PO₄)₃ synthesized using hydrogen as the reducing agent was 127 mA h g⁻¹ and decreased to 120 mA h g⁻¹ after 20 charge-discharge cycles. The substitution of lithium and vanadium for other ions did not result in the improvement of the electrochemical characteristics of the samples.     

The synthesis and lithium intercalation electrochemistry of VO2(B) ultra-thin nanowires

Ultra-thin (<10 nm diameter) VO₂(B) nanowires have been synthesised, characterised structurally and morphologically and their lithium intercalation electrochemistry investigated. The wires exist in bundles and exhibit significant preferred orientation. They have a capacity to intercalate lithium of 265 mAh g⁻¹ (Li_0.82VO₂(B)) at a rate of 10 mA g⁻¹ compared with thicker wires of 50–100 nm diameter which exhibit a capacity of 200 mAh g⁻¹ at the same rate. The load curves, structure and morphology remain stable on cycling.     

Structural and electrochemical behavior of LiMn0.4Ni0.4Co0.2O2

Layered LiMn_0.4Ni_0.4Co_0.2O₂ with the α-NaFeO₂ structure was synthesized by the “mixed hydroxide” method, followed by a high temperature calcination at 800 °C giving a single phase material of surface area 5 m² g⁻¹. A combined X-ray/neutron diffraction Rietveld refinement showed that the transition metals in the 3b layer are randomly distributed at room temperature, and that only nickel migrates to the lithium layer and in this case 4.4%. Addition of excess lithium reduces the amount of nickel on the lithium sites. The magnetic susceptibilities of the compounds LiMn_yNi_yCo_1−2yO₂ (y = 0.5, 0.4, 0.333) follow the Curie–Weiss law above 100 K and are consistent with the presence of Ni²⁺, Mn⁴⁺ and Co³⁺ cations; their magnetization curves, measured at 5 K and showing a pronounced hysteresis, are also consistent with the nickel content on the lithium sites increasing with decreasing cobalt content. This material shows a stable capacity of 140–170 mA h g⁻¹ for more than 90 cycles within the voltage window of 2.5–4.4 V. The layered rhombohedral structure is maintained as lithium is removed down to at least a lithium content of 0.05; the total volume change on cycling is under 2%. The nickel ions pin the lattice so that MO₂ slab sliding to form the 1T structure cannot readily occur. The capability of aqueous acids to leach lithium from the lattice decreases with increasing nickel content in the lithium layer; however, the thermal stability of the delithiated compounds increases with cobalt content.     

Anode properties of thick-film electrodes prepared by gas deposition of Ni-coated Si particles

Thick-film electrodes of Si particles coated with Ni, Ni-Sn, and Ni-P were fabricated by electroless deposition followed by gas deposition to form the anode of a Li-ion battery. The electrode of Ni-coated Si showed remarkably improved cycling performance with a discharge capacity of 580 mA h g⁻¹ at the 1000th cycle, which is possibly caused by its higher elastic modulus than that of the uncoated Si electrode. The electrode of Si coated with Ni-P, which consisted of Ni₃P, with the lower coating amount exhibited a higher initial capacity and excellent cycling performance with a capacity of 790 mA h g⁻¹ at the 1000th cycle, whereas poor performance was obtained for the electrode of Si coated with Ni-Sn. The excellent performance in the case of Ni-P coating is attributed to the smaller amount of coating, the high elastic modulus, and the lower reactivity of Ni₃P with Li ions in comparison with Ni₃Sn in Ni-Sn.     

All-solid-state lithium secondary batteries with high capacity using black phosphorus negative electrode

Black phosphorus was prepared from red phosphorus by using mixer mill and planetary ball-mill apparatuses. The composites with black phosphorus and acetylene black (AB) were also prepared by using the mixer mill apparatus. The mechanical milling of black phosphorus and AB brought about a decrease in size of secondary particles of the composites. The all-solid-state lithium cells with the composite and the Li₂S-P₂S₅ glass-ceramic electrolyte exhibited the first discharge capacity of 1962 mAh g⁻¹ and the coulombic efficiency of 89% at the current density of 0.064 mA cm⁻² (24 mA g⁻¹). The all-solid-state cells worked at 3.8 mA cm⁻² (1.47 A g⁻¹) at 25 °C and showed the excellent cycle performance with a high capacity of over 500 mAh g⁻¹ for 150 cycles. Black phosphorus is one of the most attractive negative electrodes with both high capacity and high-rate performance in all-solid-state lithium rechargeable batteries with sulfide electrolytes.     

NH4V3O8/carbon nanotubes composite cathode material with high capacity and good rate capability

NH₄V₃O₈/carbon nanotubes (CNTs) composites are synthesized by one-step hydrothermal method. All the samples show the flake-like morphology with the width of up to 5 μm and thickness of 500 nm and the CNTs are clearly observed on the surface of modified NH₄V₃O₈. It is found that incorporation of 0.5 wt% CNTs into NH₄V₃O₈ could greatly improve its discharge capacity and cycling stability. It delivers a maximum discharge capacity of 358.7 mAh g⁻¹ at 30 mA g⁻¹, 55 mAh g⁻¹ larger than that of the pristine one. At 150 mA g⁻¹, the composite shows 226.2 mAh g⁻¹ discharge capacity with excellent capacity retention of 97% after 100 cycles. The much improved electrochemical performance of NH₄V₃O₈ is attributed to incorporation of CNTs, which facilitates the interface charge transfer and Li⁺ diffusion.     

(NH4)0.5V2O5 nanobelt with good cycling stability as cathode material for Li-ion battery

(NH₄)_0.5V₂O₅ nanobelt is synthesized by sodium dodecyl benzene sulfonate (SDBS) assisted hydrothermal reaction as a cathode material for Li-ion battery. The as-prepared (NH₄)_0.5V₂O₅ nanobelts are 50-200 nm in diameter and several micrometers in length. The reversible lithium intercalation behavior of the nanobelts has been evaluated by cyclic voltammetry, galvanostatic discharge-charge cycling, and electrochemical impedance spectroscopy. The (NH₄)_0.5V₂O₅ delivers an initial specific discharge capacity of 225.2 mAh g⁻¹ between 1.8 and 4.0 V at 15 mA g⁻¹, and still maintains a high discharge capacity of 197.5 mAh g⁻¹ after 11 cycles. It shows good rate capability with a discharge capacity of about 180 mAh g⁻¹ remaining after 40 cycles at various rates and excellent cycling stability with the capacity retention of 81.9% after 100 cycles at 150 mA g⁻¹. Interestingly, the excess 120 mAh g⁻¹ capacity in the first charge process is observed, most of which could be attributed to the extraction of NH₄⁺ group, verified by Fourier transform Infrared (FT-IR) and X-ray diffraction (XRD) results.     

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.     

Synthesis and electrochemical performance of Li2CoSiO4 as cathode material for lithium ion batteries

Li₂CoSiO₄ has been prepared successfully by a solution route or hydrothermal reaction for the first time, and its electrochemical performance has been investigated primarily. Reversible extraction and insertion of lithium from and into Li₂CoSiO₄ at 4.1 V versus lithium have shown that this material is a potential candidate for the cathode in lithium ion batteries. At this stage reversible electrochemical extraction was limited to 0.46 lithium per formula unit for the Li₂CoSiO₄/C composite materials, with a charge capacity of 234 mAh g⁻¹ and a discharge capacity of 75 mAh g⁻¹.     

Preparation and electrochemical properties of La0.4Sr0.6FeO3 as negative electrode of Ni/MH batteries

Perovskite-type oxide La_0.4Sr_0.6FeO₃ powder was prepared by a stearic acid combustion method, and its phase structure, kinetic characteristics, and electrochemical properties were systematically investigated as the negative electrode for Ni/MH batteries. X-ray diffraction (XRD) shows that the as-prepared powder consists of a single phase with rhombohedral structure. After 20 cycles, perovskite-type structure still remains in the electrode sample. The electrochemical test shows that the reaction at the La_0.4Sr_0.6FeO₃ electrode is reversible. With an increase in temperature from 298 K to 333 K, its initial discharge capacities increase from 153.4 mA h g⁻¹ to 502.6 mA h g⁻¹ at 31.25 mA g⁻¹, and from 56.0 mA h g⁻¹ to 279.6 mA h g⁻¹ at 125 mA g⁻¹, respectively. At a discharge current density of 125 mA g⁻¹, its capacities keep steady at about 80.0 mA h g⁻¹, 195 mA h g⁻¹ and 370 mA h g⁻¹ at 298 K, 313 K and 333 K, respectively. Both the exchange current density and the proton diffusion coefficient of the La_0.4Sr_0.6FeO₃ oxide electrode also increase with temperature in a manner similar to the discharge capacity.     

High rate capabilities of all-solid-state lithium secondary batteries using Li4Ti5O12-coated LiNi0.8Co0.15Al0.05O2 and a sulfide-based solid electrolyte

Rate capability of LiNi_0.8Co_0.15Al_0.05O₂ in solid-state cells was investigated with 70Li₂S-30P₂S₅ glass-ceramics as a sulfide solid electrolyte. It showed higher rate capability than LiCoO₂; discharge capacity observed at a current density of 10 mA cm⁻² was ca. 70 mAh g⁻¹. Surface coating with Li₄Ti₅O₁₂ onto the LiNi_0.8Co_0.15Al_0.05O₂ particles further improved the high-rate performance to give ca. 110 mAh g⁻¹. The rate capability promises to realize all-solid-state lithium secondary batteries with very high performance.     

Li4Ti5O12/Sn composite anodes for lithium-ion batteries: Synthesis and electrochemical performance

Li₄Ti₅O₁₂/tin phase composites are successfully prepared by cellulose-assisted combustion synthesis of Li₄Ti₅O₁₂ matrix and precipitation of the tin phase. The effect of firing temperature on the particulate morphologies, particle size, specific surface area and electrochemical performance of Li₄Ti₅O₁₂/tin oxide composites is systematically investigated by SEM, XRD, TG, BET and charge-discharge characterizations. The grain growth of tin phase is suppressed by forming composite with Li₄Ti₅O₁₂ at a calcination of 500 °C, due to the steric effect of Li₄Ti₅O₁₂ and chemical interaction between Li₄Ti₅O₁₂ and tin oxide. The experimental results indicate that Li₄Ti₅O₁₂/tin phase composite fired at 500 °C has the best electrochemical performance. A capacity of 224 mAh g⁻¹ is maintained after 50 cycles at 100 mA g⁻¹ current density, which is still higher than 195 mAh g⁻¹ for the pure Li₄Ti₅O₁₂ after the same charge/discharge cycles. It suggests Li₄Ti₅O₁₂/tin phase composite may be a potential anode of lithium-ion batteries through optimizing the synthesis process.     

Effect of annealing on the electrochemical properties of ramsdellite-type lithium titanium oxide

Lithium titanium oxide (LTO) with a ramsdellite structure is an advantageous anode for lithium ion secondary batteries, because of its positive potential, which is beneficial for safety reasons. In addition, compared with other titanate anodes, it has a superior theoretical capacity of 321 mA h g⁻¹, which is close to the capacity of a practical carbonaceous anode. Our study showed that this ramsdellite-type LTO had a high discharge capacity that is stable at 250 mA h g⁻¹ at a current density of 1 mA cm⁻². However, this high capacity is only achieved by employing as-synthesized ramsdellite LTO powder. When the same powder was stored and the same evaluation was carried out, the resulting capacity was 200 mA h g⁻¹, which is lower than the capacity of as-synthesized powder. An annealing applied to the ramsdellite LTO powder appeared to restore the capacity loss after storage. Annealing at 250 °C for 5 h produced the best performance, which was even better than that obtained using the as-synthesized ramsdellite LTO powder. Moreover, we investigated the surface property of ramsdellite LTO and found that the presence of a carbon derivative is apparently responsible for blocking the Li ions insertion/extraction, and thus reducing the capacity.     

Structural and electrochemical properties of Cl-doped LiFePO4/C

Cl-doped LiFePO₄/C cathode materials were synthesized through a carbothermal reduction route, and the microstructure and electrochemical performances were systematically studied. Cl-doped LiFePO₄/C cathode materials presented a high discharge capacity of ∼90 mAh g⁻¹ at the rate of 20 C (3400 mA g⁻¹) at room temperature. Electrochemical impedance spectroscopy and cyclic voltamperometry indicated the optimized electrochemical reaction and Li⁺ diffusion in the bulk of LiFePO₄ due to Cl-doping. The improved Li⁺ diffusion capability is attributed to the microstructure modification of LiFePO₄ via Cl-doping.