Fibrous polyaniline as positive active material in lithium secondary batteries

Fibrous polyaniline (f-PANI) has displayed a maximum discharge capacity of 164 A h kg⁻¹, a low rate of self-discharge, and a long life as a positive active material in a secondary lithium battery.     

Lithium intercalation behavior into iron cyanide complex as positive electrode of lithium secondary battery

Lithium intercalation of iron cyanide Prussian blue, Fe₄[Fe(CN)₆]₃·xH₂O, in an aprotic media was examined in regard to the water content inside the lattice. Prussian blue showed reversible lithium intercalation potential around 3 V vs. Li, which corresponds to a redox of iron ions. Two types of water molecules were contained in the structure, one of which called zeolitic water has little effect on lithium intercalation and the theoretical capacity was always observed regardless of its amount. Other coordinating water molecules surrounding Fe³⁺ ions were necessary for the lithium intercalation and their removal by drying beyond 200°C led to a significant capacity decrease.     

A key technology to improve the cyclic performances of carbonaceous materials for lithium secondary battery anodes

Any carbonaceous material does not necessarily provide a favorable surface fora smooth electrochemical lithium doping/undoping reaction because the carbon surface is covered with a very thin inhibiting surface layer. Especially, carbonaceous materials prepared at lower temperatures exhibit very poor charge/discharge cycleability. Removing such a surface layer was found quite effective to provide very favorable electrode surfaces for the doping/undoping reaction. Simple heating of the pristine sample in vacuum was effective, but a more effective and versatile method was a mild oxidation treatment at a moderate temperature only for several minutes. Upon being treated with the mild oxidation, the cycleability as well as high rate capacity of carbonaceous materials were improved to a great extent. A trace amount of water contained in nonaqueous electrolyte was also found to deteriorate the electrochemical properties, which was ascribed to the formation of retarding surface film such as LiOH through the reduction reaction with lithium cation and water during charging.     

Preparation of carbon-coated Sn powders and their loading onto graphite flakes for lithium ion secondary battery

Carbon-coated Sn powders were prepared from the powder mixtures of thermoplastic precursor PVA, SnO₂ and MgO. The characterization of composite powders synthesized was carried out by XRD, TG, TEM, SEM and anodic performance measurement. SnO₂ was reduced to metallic Sn by heating with PVA, and its particle size in carbon shell was around 30–100 nm. MgO existence hindered the agglomeration of molten metallic Sn and made the dispersion of metallic Sn as fine particles possible. They showed high anodic performance in lithium ion batteries; high charge capacity as 500 mAh g⁻¹ even after tenth cycle and stable cyclic performance. The spaces left in carbon shell by MgO after its dissolution were supposed to absorb a large volume expansion of Sn metal particle by Li alloying during discharging. When carbon-coated Sn loaded onto graphite flakes, metallic tin contributed to the increase in capacity.     

Electrochemical synthesis of new substituted manganese oxides for lithium battery applications

New Co- and Al-substituted manganese dioxide materials have been prepared by electrochemical synthesis under hydrothermal conditions. The hollandite (α), pyrolusite (β) and γ structures can be stabilized using different experimental conditions. For each structure, the substitution leads to nanostructured compounds with various morphologies made of nanosized crystals and to much larger surface areas. Some substituted compounds display larger reversible Li insertion capacities than their non-substituted parents compounds.     

Plates soaking prior formation and its influence on positive active material phase composition and battery performance

In the present work, we studied the behaviour of 3BS and lead oxide paste as a function of soaking time in two sulfuric acid solutions respectively with 1.05 and 1.20 g cm⁻³ specific gravity. The study was based on X-ray diffraction analysis (XRD), thermogravimetry (TG), differential scanning calorimetry (DSC) and chemical analysis. The results showed that during plates soaking, 3BS and PbO are converted to monobasic lead sulphate (1BS) and lead sulphate (PbSO₄). During plate formation in 1.05 s.g. H₂SO₄ solution, these compounds are oxidized to PbO₂, the XRD patterns showed that the longer is the time of plates soaking prior formation the lower is α-PbO₂ content in positive active material. On forming, PbSO₄ crystals convert to β-PbO₂ whereas α-PbO₂ is a result of 3BS oxidation. The capacity and cycle life of PAM decrease with soaking time, the concentration of the H₂SO₄ solution during soaking exerts stronger influence than the duration of soaking.     

Electrochemical behavior of plasma-fluorinated graphite for lithium ion batteries

Electrochemical properties of plasma-fluorinated graphite samples have been investigated in 1 mol dm⁻³ LiClO₄ ethylene carbonate (EC)/diethyl carbonate (DEC) solution at 25 °C. Fluorine contents in plasma-fluorinated graphite samples were in the range of 0–0.3 at.% by elemental analysis and surface fluorine concentrations obtained by X-ray photoelectron spectroscopy (XPS) were in the range of 3–12 at.%. Raman spectroscopy revealed that surface disordering of graphite was induced by plasma fluorination. Plasma treatment increased the surface areas of graphite samples by 26–55% and the pore volumes for the mesopores with diameters of 1.5–2 and 2–3 nm. Plasma-fluorinated graphites showed capacities higher than those of original graphites and even higher than the theoretical capacity of graphite, 372 mAh g⁻¹, without any change of the profile of charge–discharge potential curves. The increments in the capacities were approximately 5, 10 and 15% for graphites with average particle diameters, 7, 25 and 40 μm, respectively. Furthermore, the coulombic efficiencies in first cycle were nearly the same as those for original graphites or higher by several percents.     

Influence of positive active material type and grid alloy on corrosion layer structure and composition in the valve regulated lead/acid battery

Performance of a valve regulated lead/acid battery is affected by the properties of the positive grid corrosion layer. An investigation has been carried out using a range of experimental techniques to study the influence of corrosion layer composition and structure on cyclic performance. A number of designs of battery were manufactured with different grids and positive active materials (PAMs). Two grid types were used consisting of either pure lead or a lead/tin alloy. Variations in PAM composition and structure were obtained by forming electrodes from grey oxide pastes containing additions of, red lead, tetrabasic lead sulphate, or sulphuric acid (sulphated). Results indicated that both grid alloy composition and PAM type affect the corrosion layer properties. Ultra-microtoming was used to prepare sections of the grid/corrosion layer interface. Results showed that corrosion propagated along tin rich grain boundaries.     

Electrochemical synthesis of macroporous aluminium films and their behavior towards lithium deposition/stripping

In the present study macroporous aluminium electrodes were made by template assisted electrodeposition from ionic liquids. Polystyrene (PS) spheres (diameter 600 nm) were applied onto polished copper electrodes by immersion into an alcoholic suspension containing PS spheres. Al was deposited from the chloroaluminate ionic liquid [EMIm]Cl/AlCl₃ (40/60 mol.%) on this substrate. After chemical dissolution of the PS spheres a macroporous aluminium electrode was obtained which served as a host material for Li deposition from ionic liquids. Lithium deposition in this matrix is reversible showing certain activation with an increasing number of cycles. After 10 cycles of Li deposition/dissolution the macroporous structure is still visible.     

Novel hedgehog-like 5 V LiCoPO4 positive electrode material for rechargeable lithium battery

Hedgehog-like LiCoPO₄ with hierarchical microstructures is first synthesized via a simple solvothermal process in water-benzyl alcohol mixed solvent at 200 °C. Morphology and crystalline structure of the samples are characterized by scanning electron microscope, transmission electron microscopy and X-ray diffraction. The hedgehog-like LiCoPO₄ microstructures in the size of about 5-8 μm are composed of large numbers of nanorods in diameter of ca. 40 nm and length of ca. 1 μm, which are coated with a carbon layer of ca. 8 nm in thickness by in situ carbonization of glucose during the solvothermal reaction. As a 5 V positive electrode material for rechargeable lithium battery, the hedgehog-like LiCoPO₄ delivers an initial discharge capacity of 136 mAh g⁻¹ at 0.1 C rate and retains its 91% after 50 cycles, showing much better electrochemical performances than sub-micrometer LiCoPO₄ synthesized by conventional high-temperature solid-state reaction.     

A novel structure of ceramics electrolyte for future lithium battery

In order to fabricate large scale all-solid-state Li battery, we suggested a novel structure of solid electrolyte, which is composed of porous electrolyte supported by honeycomb-type electrolyte. A possibility of fabrication of the honeycomb-supported porous electrolyte and a compatibility of this structure with all-solid-state battery were examined using LLT (Li_0.35La_0.55TiO₃) solid electrolyte which is one of the anticipated solid electrolytes due to its high Li ion conductivity. A porous layer membrane with 3 dimensionally ordered (3DOM) macroporous structure was prepared by a colloidal crystal templating method. The porous honeycomb was fabricated by pushing the membrane into holes of honycomb using a needle followed by calcination. The 3DOM membrane and honeycmb electrolyte were sintered well each other. After filling the 3DOM pores with LiMn₂O₄ cathode material, the compatibility of this novel porous honeycomb electrolyte with all-solid-state battery was examined. The LiMn₂O₄/porous honeycomb cell clearly demonstrated charge and discharge behaviors, indicating the porous honeycomb structure can be applied to the all-solid-state battery. The discharge capacity was 71 mA h g⁻¹ (1.3 mA h cm⁻²) at 30 °C.     

Electrochemical characteristics of aluminum sulfide for use in lithium secondary batteries

In our effect to develop a lithium secondary battery with high energy density, aluminum sulfide (Al₂S₃) was studied for use as an active material. The measured initial discharge capacity of Al₂S₃ was ca. 1170 mAh g⁻¹ at 100 mA g⁻¹. This corresponds to 62% of the theoretical capacity for the sulfide. Al₂S₃ exhibited poor capacity retention in the potential range between 0.01 V and 2.0 V, mainly due to the structural irreversibility of the charge process or Li extraction. XRD and Al and S K-XANES analyses indicated that the surface of Al₂S₃ reacts reversibly during charge and discharge processes, while the core of Al₂S₃ showed structural irreversibility because LiAl and Li₂S were formed from Al₂S₃ at the initial discharge and remained as they were afterward.     

Electrochemical properties of new organic radical materials for lithium secondary batteries

The use of ionic liquid (IL)-supported organic radicals as cathode-active materials in lithium secondary batteries is reported in this article. Two different types of IL-supported organic radicals based on the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical and imidazolium hexafluorophosphate IL were synthesized. The first type is a mono-radical with one unit of TEMPO and the second is a symmetrical di-radical with 2 U of TEMPO; both are viscous liquids at 25 °C. The radicals exhibit electrochemical activity at ∼3.5 V versus Li/Li⁺ as revealed in the cyclic voltammetry tests. The organic radical batteries (ORBs) with these materials as the cathode, a lithium metal anode and 1 M LiPF₆ in EC/DMC electrolyte exhibited good performance at room temperature during the charge–discharge and cycling tests. The batteries exhibited specific capacities of 59 and 80 mAh g⁻¹ at 1 C-rate with the mono- and di-radicals as the cathodes, respectively, resulting in 100% utilization of the materials. The performance degradation with increasing C-rate is very minimal for the ORBs, thus demonstrating good rate capability.     

A new lithium salt with dihydroxybenzene and lithium tetrafluoroborate for lithium battery electrolytes

A new unsymmetrical lithium salt containing F⁻, C₆H₄O₂²⁻ [dianion of 1,2-benzenediol], lithium difluoro(1,2-benzene-diolato(2-)-o,o′)borate (LDFBDB) is synthesized and characterized. Its thermal decomposition in nitrogen begins at 170 °C. The cyclic voltammetry study shows that the LDFBDB solution in propylene carbonate (PC) is stable up to 3.7 V versus Li⁺/Li. It is soluble in common organic solvents. The ionic dissociation properties of LDFBDB are examined by conductivity measurements in PC, PC+ ethyl methyl carbonate (EMC), PC + dimethyl ether (DME), PC + ethylene carbonate (EC) + EMC solutions. The conductivity values of the 0.564 mol dm⁻³ LDFBDB electrolyte in PC + DME solution is 3.90 mS cm⁻¹. All these properties of the new lithium salt including the thermal characteristics, electrochemical stabilities, solubilities, ionic dissociation properties are studied and compared with those of its derivatives, lithium difluoro(3-fluoro-1,2-benzene-diolato(2-)-o,o′)borate (FLDFBDB), lithium [3-fluoro-1,2-benzenediolato(2-)-o,o′ oxalato]borate (FLBDOB), and lithium bis(oxalate)borate (LBOB).     

Electrochemical stability of core–shell structure electrode for high voltage cycling as positive electrode for lithium ion batteries

The core–shell type cathode material Li[(Ni_0.8Co_0.1Mn_0.1)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ (CS) for Li-ion battery was synthesized via co-precipitation method. The electrochemical and thermal properties of the core–shell structured Li[(Ni_0.8Co_0.1Mn_0.1)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ were compared with those of the average composition of core–shell Li[Ni_0.74Co_0.08Mn_0.18]O₂ (ACCS) and the mixture of the core Li[Ni_0.8Co_0.1Mn_0.1]O₂ and the shell Li[Ni_0.5Mn_0.5]O₂ material (MCS). The CS shows the enhanced electrochemical properties in a high voltage range (4.5 V and 4.6 V) as well as the typical cut-off voltage range (4.3 V). The capacity retentions of CS, core, and ACCS material were 94.2% (176.9 mAh g⁻¹), 86.6% (172 mAh g⁻¹), and 88.4% (169.3 mAh g⁻¹) after 120 cycles, respectively.     

Development of efficient carbon anode material for a high-power and long-life lithium ion battery

The Li ion battery with high power and long life is required for the hybrid electronic vehicle. A new carbon anode material called “ICOKE” has been prepared by the graphitization of coke at ca. 2000 °C and is shown to have excellent pulse charge/discharge characteristics and long cycle performance. The charge/discharge reaction mechanism of ICOKE was investigated in detail based on the result of cyclic voltammetry and X-ray diffraction profile change of ICOKE before and after charging. As a result, it was found that Li-intercalation reaction to ICOKE proceeds without forming higher stage compounds and the 1st and the 2nd stage compounds are directly formed.     

New lithium salts with croconato-complexes of boron for lithium battery electrolytes

A new lithium salt containing C₅O₅²⁻, lithium bis[croconato]borate (LBCB), and its novel derivative, lithium [croconato salicylato]borate (LCSB) were synthesized and characterized. The thermal characteristics of them and lithium bis[salicylato(2-)]-borate (LBSB) were examined by thermogravimetric analysis (TG). The thermal decomposition in Ar begins at 250, 328, and 350 °C for LBCB, LCSB, and LBSB, respectively. The order of the stability toward oxidation of these organoborates is LBCB > LCSB > LBSB, which differs from the thermal stability. The cyclic voltammetry study shows that the LiBCB and LCSB solutions in PC are stable up to 5.5 and 4.8 V versus Li⁺/Li, respectively. They are moderately soluble in common organic solvents, being 0.14, 0.16, and 1.4 mol dm⁻³ at 20 °C in EC + DME (molar ratio 1:1) for LBCB, LCSB, and LBSB, respectively. Ionic dissociation properties of LBCB and its derivatives were examined by conductivity measurements in PC, PC + DME, EC + DME, PC + THF, EC + THF (molar ratio 1:1) solutions. The conductivity values of the 0.10 mol dm⁻³ LBCB electrolyte in PC, PC + DME, EC + DME, PC + THF, EC + THF solutions are higher than those of LCSB and LBSB electrolytes. It means that LBCB has the higher dissociation ability in those solutions.     

Surface structure and electrochemical characteristics of plasma-fluorinated petroleum cokes for lithium ion battery

Plasma-fluorination of petroleum coke and those heat-treated at 1860, 2300 and 2800 °C (abbreviated to PC, PC1860, PC2300 and PC2800) was conducted for 15, 30 and 60 min using CF₄ gas at 90 °C. Fluorine contents obtained by elemental analysis were negligible except PC fluorinated for 60 min (0.7 at.%). Fluorine concentration on the surface decreased with increasing heat-treatment temperature of petroleum coke, i.e. from PC to PC2800 when plasma-fluorination was made for 30 and 60 min. Transmission electron microscopic observation revealed that the closed edges of PC2800 were destroyed and opened by plasma-treatment. Plasma-fluorination increased surface disorder of heat-treated petroleum cokes, however, slightly reduced surface areas. These surface structure changes increased first coulombic efficiencies of PC2300 and PC2800 by 6–8 and 8–10% at both 60 and 150 mA g⁻¹, respectively.