Highly promoted electrochemical performance of 5 V LiCoPO4 cathode material by addition of vanadium

Li_1+0.5xCo_1−xV_x(PO₄)_1+0.5x/C (x = 0, 0.05, 0.10) composites with ordered olivine structure have been synthesized for use as cathode material in lithium ion batteries. The morphology and microstructure are characterized by scanning electron microscope, transmission electron microscopy and X-ray diffraction. The electrochemical test results show that addition of vanadium into LiCoPO₄ remarkably improves its charge and discharge behavior. Li_1.025Co_0.95V_0.05(PO₄)_1.025/C electrode gives its initial discharge capacity of 134.8 mAh g⁻¹ at 0.1 C current rate, against 112.2 mAh g⁻¹ for the pristine LiCoPO₄/C, and exhibits much better cyclic stability than the latter. In particular, vanadium doping leads to an enhancement of the discharge voltage plateau for about 70 mV.     

An application of lithium cobalt nickel manganese oxide to high-power and high-energy density lithium-ion batteries

Evolved gas analysis (EGA) by mass spectroscopy (MS) was carried out for the pyrolysis of Li_1−xCo_1/3Ni_1/3Mn_1/3O₂ (185 mAh g⁻¹ of charge capacity) and the results were compared with that of Li_1−xCoO₂ (140 mAh g⁻¹). Electrochemically prepared Li_1−xCo_1/3Ni_1/3Mn_1/3O₂ clearly shows that O₂ evolution begins at much higher temperature than Li_1−xCoO₂, suggesting that Li_1−xCo_1/3Ni_1/3Mn_1/3O₂ is superior to LiCoO₂ with respect to thermal stability. High-temperature XRD measurements of charged LiCo_1/3Ni_1/3Mn_1/3O₂-electrodes at 4.45 V were also carried out and shown that the decomposition product by heating was identified as a cubic spinel consisting of cobalt, nickel, and manganese. This indicates that phase change from a layered to spinel-framework structure plays a crucial role in the suppression of oxygen evolution from the solid matrix. In order to show practicability of the new material, lithium-ion batteries with graphite-negative electrodes are fabricated and examined in the R18650-hardware. The new lithium-ion batteries show high rate discharge performances, excellent cycle life, and safety together with high-energy density.     

Fine cathode particles prepared by solid-state reaction method using nano-sized precursor particles

Fine-sized Li–Co–Mn–O cathode particles with various ratios of cobalt and manganese components were prepared by conventional solid-state reaction method using the nano-sized precursor particles. The nano-sized precursor particles of cobalt and manganese components were prepared by spray pyrolysis. The LiCo_1−xMn_xO₂ (0.1 ≤ x ≤ 0.3) particles had finer size than that of the pure LiCoO₂ particles. Manganese component disturbed the growth of the LiCo_1−xMn_xO₂ cathode particles prepared by solid-state reaction method. The initial discharge capacities of the layered LiCo_1−xMn_xO₂ (0 ≤ x ≤ 0.3) cathode particles decreased from 144 to 136 mAh g⁻¹ when the ratios of Co/Mn components were changed from 1/0 to 0.7/0.3. The mean sizes of the spinel LiMn_2−yCo_yO₄ (0 ≤ y ≤ 0.2) cathode particles decreased from 650 to 460 nm when the ratios of Mn/Co components were changed from 2/0 to 1.8/0.2. The initial discharge capacities of the LiMn_2−yCo_yO₄ (0 ≤ y ≤ 0.2) cathode particles decreased from 119 to 86 mAh g⁻¹ when the ratios of Mn/Co components were changed from 2/0 to 1.8/0.2.     

Electrochemical properties of doped lithium titanate compounds and their performance in lithium rechargeable batteries

Several substituted titanates of formula Li_4−xMg_xTi_5−xV_xO₁₂ (0 ≤ x ≤ 1) were synthesized (and investigated) as anode materials in rechargeable lithium batteries. Five samples labeled as S1–S5 were calcined (fired) at 900 °C for 10 h in air, and slowly cooled to room temperature in a tube furnace. The structural properties of the synthesized products have been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transmission infrared (FTIR). XRD explained that the crystal structures of all samples were monoclinic while S1 and S3 were hexagonal. The morphology of the crystal of S1 was spherical while the other samples were prismatic in shape. SEM investigations explained that S4 had larger grain size diameter of 15–16 μm in comparison with the other samples. S4 sample had the highest conductivity 2.452 × 10⁻⁴ S cm⁻¹. At a voltage plateau located at about 1.55 V (vs. Li ⁺), S4 cell exhibited an initial specific discharge capacity of 198 mAh g⁻¹. The results of cyclic voltammetry for Li_4−xMg_xTi_5−xV_xO₁₂ showed that the electrochemical reaction was based on Ti⁴⁺/Ti³⁺ redox couple at potential range from 1.5 to 1.7 V. There is a pair of reversible redox peaks corresponding to the process of Li⁺ intercalation and de-intercalation in the Li–Ti–O oxides.     

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.     

Electrochemical behaviour of Heusler alloy Co2MnSi for secondary lithium batteries

Electrochemical lithiation of Co₂MnSi with a Heusler structure is investigated as a candidate negative electrode (anode) material for secondary lithium batteries. The electrode maintains a reversible discharge capacity of 112 mAh g⁻¹ for 50 cycles when cycled between 0.01 and 3 V. It is proposed that the lithiation mechanism consists of two steps. Co₂MnSi transforms to Heusler-type Li₂MnSi during the first charge cycle and subsequent charge–discharge cycles involve the formation of a solid solution in Li_xMnSi. The latter compound maintains its structural integrity throughout cycling to provide steady cycling behaviour. Magnetic measurements are also employed to substantiate further the structural changes during electrochemical cycling.     

Temperature-controlled microwave solid-state synthesis of Li3V2(PO4)3 as cathode materials for lithium batteries

Monoclinic Li₃V₂(PO₄)₃ can be rapidly synthesized at 750 °C for 5 min (MW5m) by using temperature-controlled microwave solid-state synthesis method (TCMS). The carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage 3.0-4.3, MW5m presents a charge capacity 132 mAh g⁻¹, almost equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹), and discharge capacity 126.4 mAh g⁻¹. In the cut-off voltage 3.0-4.8 V, MW5m shows an initial discharge capacity of 183.4 mAh g⁻¹, near to the theoretical discharge capacity. In the cycle performance, the capacity fade of Li₃V₂(PO₄)₃ is dependent on the cut-off voltage and the preparation method.     

Synthesis, phase relation and electrical and electrochemical properties of ruthenium-substituted Li2MnO3 as a novel cathode material

Layered oxides, ruthenium-substituted Li₂MnO₃, were synthesized at 800 °C and 1200 °C. Their phase relation and electrical and electrochemical properties were investigated. Li₂Mn_1−xRu_xO₃ synthesized at 800 °C clearly separated into two phases, manganese-rich and ruthenium-rich phases, except for the narrow composition range of 0 ≤ x ≤ 0.05, while Li₂Mn_1−xRu_xO₃ synthesized at 1200 °C formed two solid solutions in the whole composition range across a structural transition between x = 0.6 and 0.8. The electrical resistivity of Li₂Mn_1−xRu_xO₃ decreased with increasing ruthenium content. Li₂Mn_0.2Ru_0.8O₃ (x = 0.8) synthesized at 1200 °C showed the lowest resistivity of 5.7 × 10² Ω cm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li₂Mn_0.4Ru_0.6O₃ (x = 0.6) exhibited a discharge capacity of 192 mAh g⁻¹ in the initial cycle and 169 mAh g⁻¹ in the tenth cycle with high and almost constant charge-discharge efficiencies of 99% from the second to tenth cycle at a current rate of 1/10C. The ruthenium substitution to Li₂MnO₃ is quite effective to improve electrical conductivity and charge-discharge performance.     

The influence of compositional change of 0.3Li2MnO3·0.7LiMn1−xNiyCo0.1O2 (0.2 ≤ x ≤ 0.5, y = x − 0.1) cathode materials prepared by co-precipitation

Cathode materials prepared by a co-precipitation are 0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (0.2 ≤ x ≤ 0.4) cathode materials with a layered-spinel structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (x = 0.3, y = 0.2) cell shows the initial discharge capacity of about 200 mAh g⁻¹. However, when x = 0.2 and y = 0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life.     

Co-doped NiO nanoflake arrays toward superior anode materials for lithium ion batteries

Co-doped NiO nanoflake arrays with a cellular-like morphology are fabricated by low temperature chemical bath deposition. As anode material for lithium ion batteries (LIBs), the array film shows a capacity of 600 mAh g⁻¹ after 50 discharge/charge cycles at low current density of 100 mA g⁻¹, and it retains 471 mAh g⁻¹ when the current density is increased to 2 A g⁻¹. Appropriate electrode configuration possesses some unique features, including high electrode-electrolyte contact area, direct contact between each naonflake and current collector, fast Li⁺ diffusion. The Co²⁺ partially substitutes Ni³⁺, resulting in an increase of holes concentration, and therefore improved p-type conductivity, which is useful to reduce charge transfer resistance during the charge/discharge process. The synergetic effect of these two parts can account for the improved electrochemical performance.     

Preparation and electrochemical properties of Li[Ni1/3Co1/3Mn1−x/3Zrx/3]O2 cathode materials for Li-ion batteries

Layer-structured Zr doped Li[Ni_1/3Co_1/3Mn_1−x/3Zr_x/3]O₂ (0 ≤ x ≤ 0.05) were synthesized via slurry spray drying method. The powders were characterized by XRD, SEM and galvanostatic charge/discharge tests. The products remained single-phase within the range of 0 ≤ x ≤ 0.03. The charge and discharge cycling of the cells showed that Zr doping enhanced cycle life compared to the bare one, while did not cause the reduction of the discharge capacity of Li[Ni_1/3Co_1/3Mn_1/3]O₂. The unchanged peak shape in the differential capacity versus voltage curve suggested that the Zr had the effect to stabilize the structure during cycling. More interestingly, the rate capability was greatly improved. The sample with x = 0.01 presented a capacity of 160.2 mAh g⁻¹ at current density of 640 mA g⁻¹(4 C), corresponding to 92.4% of its capacity at 32 mA g⁻¹(0.2 C). The favorable performance of the doped sample could be attributed to its increased lattice parameter.     

Cost-effective and ecologically safe electrolyte for lithium batteries

The electrochemical characteristic of solutions of lithium benzolsulfonate in dimethylsulfoxide is considered. DTA/TGA is employed to analyze the thermal stability of salt. The conductivity of solutions was determined. So, for example, conductivity lithium benzolsulfonate in dimethylsulfoxide is 3.8 mSm/cm. The area electrochemical stability of solutions is in an interval 4.5–4.6 V. Electrochemical properties of lithium manganese oxide spinel in tested solutions were investigated. The charge–discharge capacity of lithium manganese oxide spinel is 65 mAh g⁻¹ (in interval of potentials from 3.2 to 4.4 V Li/Li⁺) and 190 mAh g⁻¹ (in interval of potentials from 1.8 to 4.0 V Li/Li⁺) for vanadium oxide (V).     

Synthesis and electrochemical performance of the high voltage cathode material Li[Li0.2Mn0.56Ni0.16Co0.08]O2 with improved rate capability

The high voltage layered Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode material, which is a solid solution between Li₂MnO₃ and LiMn_0.4Ni_0.4Co_0.2O₂, has been synthesized by co-precipitation method followed by high temperature annealing at 900 °C. XRD and SEM characterizations proved that the as prepared powder is constituted of small and homogenous particles (100-300 nm), which are seen to enhance the material rate capability. After the initial decay, no obvious capacity fading was observed when cycling the material at different rates. Steady-state reversible capacities of 220 mAh g⁻¹ at 0.2C, 190 mAh g⁻¹ at 1C, 155 mAh g⁻¹ at 5C and 110 mAh g⁻¹ at 20C were achieved in long-term cycle tests within the voltage cutoff limits of 2.5 and 4.8 V at 20 °C.     

Polytriphenylamine: A high power and high capacity cathode material for rechargeable lithium batteries

Polytriphenylamine (PTPAn) was chemically synthesized and tested as a cathode material for high-rate storage and delivery of electrochemical energy. It is found that the polymer has not only superior high power capability but also high energy density at prolonged cycling. At a moderate rate of 0.5C, PTPAn gives a high average discharge voltage of 3.8 V and quite a high capacity of 103 mAh g⁻¹, which is very close to the theoretical capacity (109 mAh g⁻¹) as expected from one electron transfer per triphenylamine monomer. Even cycled at a very high rate of 20C, the polymer can still deliver a capacity of 90 mAh g⁻¹ at 1000th cycle with a nearly 100% coulombic efficiency. The excellent electrochemical performances of PTPAn are explained from the structural specificity of the polymer where the radical redox centers are stabilized and protected by conductive polymeric backbone, making the radical redox and charge-transporting processes kinetically facile for high-rate charge and discharge.     

Electrochemical performances of BiSbO4 as electrode material for lithium batteries

We present an electrochemical study of BiSbO₄, an opened layered oxide having a structure related to Aurivillius phases. Li//BiSbO₄ cells show a large specific capacity as high as 1250 mAh g⁻¹ during reduction down to 0.5 V. This reaction involves 18Li atoms per formula unit, pointing it towards a very promising cathode material for primary lithium batteries, in particular for ICD devices. The characterization of the reduction products indicates that the reduction of BiSbO₄ with lithium presumably goes along firstly with the formation of metallic Sb and Bi to follow the formation of the alloys Li₃Bi and Li₃Sb dispersed in a lithium oxide matrix. In situ X-ray diffraction experiments proved the amorphous nature of both metals and final alloys. On the other hand when Li//BiSbO₄ cells are limited to discharge down to 1.2 V, BiSbO₄ reacts with 5Li atoms. After the first discharge, that develops a specific capacity of 350 mAh g⁻¹, high cyclability has been observed.     

Hierarchical porous cobalt oxide array films prepared by electrodeposition through polystyrene sphere template and their applications for lithium ion batteries

Hierarchical porous cobalt oxide (Co₃O₄) array films are successfully prepared by electrodeposition through polystyrene sphere monolayer template. The as-prepared Co₃O₄ array films exhibit three typical porous structures from non-close-packed bowl array to close-packed bowl array and hierarchical two layer array structures. These Co₃O₄ array films have a hierarchical porous structure, in which the skeleton is composed of ordered arrays possessing nanoporous walls. A possible growth mechanism of porous Co₃O₄ array films is proposed. As anodes for Li ion batteries, the as-prepared Co₃O₄ array films exhibit quite good cycle life and high capacity. The first discharge capacity for the three Co₃O₄ array films is 1511, 1475, 1463 mAh g⁻¹, respectively, and their initial coulombic efficiencies are as high as 72%. The specific capacity after 50 cycles for the three electrodes is 712, 665 and 640 mAh g⁻¹ at 1C rate, corresponding to 80%, 75%, 72% of the theoretical value (890 mAh g⁻¹), respectively.     

Electrospun polymer membrane activated with room temperature ionic liquid: Novel polymer electrolytes for lithium batteries

A new class of polymer electrolytes (PEs) based on an electrospun polymer membrane incorporating a room-temperature ionic liquid (RTIL) has been prepared and evaluated for suitability in lithium cells. The electrospun poly(vinylidene fluoride-co-hexafluoropropylene) P(VdF-HFP) membrane is activated with a 0.5 M solution of LiTFSI in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI) or a 0.5 M solution of LiBF₄ in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄). The resulting PEs have an ionic conductivity of 2.3 × 10⁻³ S cm⁻¹ at 25 °C and anodic stability at >4.5 V versus Li⁺/Li, making them suitable for practical applications in lithium cells. A Li/LiFePO₄ cell with a PE based on BMITFSI delivers high discharge capacities when evaluated at 25 °C at the 0.1C rate (149 mAh g⁻¹) and the 0.5C rate (132 mAh g⁻¹). A very stable cycle performance is also exhibited at these low current densities. The properties decrease at the higher, 1C rate, when operated at 25 °C. Nevertheless, improved properties are obtained at a moderately elevated temperature of operation, i.e. 40 °C. This is attributed to enhanced conductivity of the electrolyte and faster reaction kinetics at higher temperatures. At 40 °C, a reversible capacity of 140 mAh g⁻¹ is obtained at the 1C rate.     

Hybrid microwave synthesis and characterization of the compounds in the Li–Ti–O system

Hybrid microwave synthesis has been applied for preparation of Li₄Ti₅O₁₂, Li₂Ti₃O₇, Li₂TiO₃ and LiTiO₂ for the first time. Stepwise heating was used for avoiding the instantaneous release of gas by-product and obtaining well-shaped samples. The samples were characterized by powder X-ray diffraction, energy-dispersive X-ray analysis and scanning electron microscopy. The obtained samples have relatively uniform particle sizes. The electrochemical performance of Li₄Ti₅O₁₂ and Li₂Ti₃O₇ were investigated. The first discharge capacity of Li₄Ti₅O₁₂ was 150 mAh g⁻¹ and 141 mAh g⁻¹ after 27 cycles and a very flat discharge and charge curve of Li₄Ti₅O₁₂ was shown at about 1.56 V. Similarly, Li₂Ti₃O₇ exhibits good cycle performance. The initial discharge capacity is 118 mAh g⁻¹ and 30th cycle is still 112 mAh g⁻¹.     

Microwave synthesis of novel high voltage (4.6 V) high capacity LiCuxCo1−xO2±δ cathode material for lithium rechargeable cells

Layered LiCu_xCo_1−xO_2±δ (0.0 ≤ x ≤ 0.3) has been synthesized using microwave method. This method possesses many advantages such as homogeneity of final product and shorter reaction time compared to other conventional methods. The structure and electrochemical properties of the synthesized materials are characterized through various methods such as XRD, SEM, FTIR, XPS and galvanostatic charge/discharge studies. The XRD patterns of LiCu_xCo_1−xO_2±δ confirm the formation of single-phase layered material. SEM images show that the particles are agglomerated and the average particle size decreases with increasing amount of copper. Electrochemical cycling studies are carried out between 2.7 and 4.6 V using 1 M LiPF₆ in 1:1 EC/DEC as electrolyte. The charge/discharge cycling studies of layered material with LiCu_0.2Co_0.8O₁₉ exhibit an average discharge capacity of ∼150 mAh g⁻¹ over the investigated 50 cycles.     

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.