Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel

LiNi_0.5Mn_1.5O₄ material with a spinel structure is prepared by a sol–gel method. The material is initially fired at 850 °C and then subjected to a post-reaction annealing at 600 °C in order to minimize the nickel deficiency. The elevated firing temperature produces materials with a small surface-area which is beneficial for good capacity retention. Indeed, the spinel LiNi_0.5Mn_1.5O₄ not only shows a good cycle performance, but exhibits an excellent discharge capacity, i.e. 114 mAh g⁻¹ at 4.66 V plateau and 127 mAh g⁻¹ in total. Cyclic voltammetry and ac impedance spectroscopy are employed to characterize the reactions of lithium insertion and extraction in the LiNi_0.5Mn_1.5O₄ electrode. Excellent electrochemical performance and low material cost make this compound an attractive cathode for advanced lithium batteries.     

Electrochemical characteristics of room temperature Li/FeS2 batteries with natural pyrite cathode

Electrochemical characteristics of Li/FeS₂ batteries having natural pyrite as cathode and liquid electrolytes have been studied at room temperature. The organic electrolytes used were 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in tetra(ethylene glycol) dimethyl ether (TEGDME) or a mixture of TEGDME and 1,3-dioxolane (DOX), and 1 M LiPF₆ in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The pyrite powder and FeS₂ cathode were characterized by SEM, EDS, XRD and charge/discharge cycling. The discharge capacities of Li/FeS₂ cells with 1 M LiTFSI dissolved in TEGDME were 772 mAh g⁻¹ at the 1st cycle and 313 mAh g⁻¹ at the 25th cycle at 0.1C. The cycling performance could be improved by using a mixture of TEGDME and DOX as the electrolyte. It was found that TEGDME contributed to high initial discharge capacity, whereas, DOX contributed to better stabilization of the performance. The first discharge capacities of Li/FeS₂ cells showed a decreasing trend with higher current densities (615 and 534 mAh g⁻¹, respectively, at 0.5C and 1.0C). Li/FeS₂ cells with the battery grade electrolyte 1 M LiPF₆ in EC/DMC had lower initial discharge capacity and cycling capability compared to the TEGDME system. The natural pyrite cathode with 1 M LiTFSI dissolved in a mixture of TEGDME and DOX showed reasonably good first discharge capacity and overall cycling performance, suitable for application in room temperature lithium batteries.     

NbSb2 as an anode material for Li-ion batteries

Polycrystalline samples of NbSb₂ have been synthesized and studied as anode material for lithium-ion batteries. The reaction mechanism of lithium with NbSb₂ is investigated by ex situ XRD and cyclic voltammogram studies. Li₃Sb and Nb are formed during first discharge and during charge lithium is extracted from Li₃Sb. The first cycle discharge capacity is 420 mA hg⁻¹ and first cycle charge capacity is 315 mA hg⁻¹.     

Lithium batteries composed of aluminate polymer complexes as single-ion conductive solid electrolytes

Single-ionic conductors, which display lithium ion migration exclusively (without anion migration), have been realized as the polymeric solid electrolytes with lithium orthoaluminate repeating units carrying oligo(oxyethylene) main chain and two side chains of endomethoxy{oligo(oxyethylene)}. The ionic conductivity of the aluminate polymer complexes is about 10⁻⁶–10⁻⁷ S/cm at room temperature. Thin film lithium secondary batteries were fabricated into 5.5 cm×4.5 cm×0.02–0.03 cm (thick) cells from lithium foil (anode), aluminate polymer complex (electrolyte) and TiS₂ (cathode). These batteries show minimal decay of output voltage upon constant current discharging and their capacity of first cycle was about 146 mA h/g of active cathode material. By contrast typical bi-ionic conductor of (aluminate polymer complex+5% LiClO₄) hybrid system showed, on the contrary, rapid decay of output voltage, due to polarization.     

Solid-state Li/LiFePO4 polymer electrolyte batteries incorporating an ionic liquid cycled at 40 °C

The cycle behaviour and rate performance of solid-state Li/LiFePO₄ polymer electrolyte batteries incorporating the N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₃TFSI) room temperature ionic liquid (IL) into the P(EO)₂₀LiTFSI electrolyte and the cathode have been investigated at 40 °C. The ionic conductivity of the P(EO)₂₀LiTFSI + PYR₁₃TFSI polymer electrolyte was about 6 × 10⁻⁴ S cm⁻¹ at 40 °C for a PYR₁₃⁺/Li⁺ mole ratio of 1.73. Li/LiFePO₄ batteries retained about 86% of their initial discharge capacity (127 mAh g⁻¹) after 240 continuous cycles and showed excellent reversible cyclability with a capacity fade lower than 0.06% per cycle over about 500 cycles at various current densities. In addition, the Li/LiFePO₄ batteries exhibited some discharge capability at high currents up to 1.52 mA cm⁻² (2 C) at 40 °C which is very significant for a lithium metal-polymer electrolyte (solvent-free) battery systems. The addition of the IL to lithium metal-polymer electrolyte batteries has resulted in a very promising improvement in performance at moderate temperatures.     

Polymeric gel electrolytes reinforced with glass-fibre cloth for lithium secondary batteries

Polymeric gel electrolytes (PGE), based on polyacrylonitrile blended with poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)), which are reinforced with glass-fibre cloth (GFC) to increase the mechanical strength, are prepared for the practical use in lithium secondary batteries. The resulting electrolytes exhibit electrochemical stability at 4.5 V against lithium metal and a conductivity value of (2.0–2.1)×10⁻³ S cm⁻¹ at room temperature. The GFC–PGE electrolytes show excellent strength and flexibility when used in batteries even if they contain a plasticiser. A test cell with LiCoO₂ as a positive electrode and mesophase pich-based carbon fibre (MCF) as a negative electrode display a capacity of 110 mAh g⁻¹ based on the positive electrode weight at the 0.2 C rate at room temperature. Over 80% of the initial capacity is retained after 400 cycles. This indicates that GFC is suitable as a reinforcing material to increase the mechanical strength of gel-based electrolytes for lithium secondary batteries.     

Electrochemical properties of the Li-ion polymer batteries with P(VdF-co-HFP)-based gel polymer electrolyte

Gel polymer electrolytes consisting of 25 wt.% P(VdF-co-HFP), 65 wt.% ethylene carbonate + propylene carbonate and 10 wt.% LiN(CF₃SO₂)₂ are prepared using by a solvent-casting technique. The electrodes are for use in lithium-ion polymer batteries. The electrochemical characteristics of the gel polymer electrolytes are evaluated by means of ac impedance and cyclic voltammetry. The charge–discharge performance of lithium polymer and lithium-ion polymer batteries is examined. A LiCoO₂ | gel polymer electrolyte (GPE) | mesocarbon microbeads (MCMB) cell delivers a discharge capacity of 146.8 and 144.5 mAh g⁻¹ on the first and the 20th cycle, respectively. The specific discharge capacity is greater than 140 mAh g⁻¹ for up to 20 cycle at all the current densities examined.     

Accelerated synthesis and electrochemical performance of Li1+x(Ni0.5Mn0.5)O2+δ cathode materials

Synthesis of Li_1+xNi_0.5Mn_0.5O_2+δ (x = 0, 0.3) cathode materials for secondary lithium batteries was performed by freeze-drying method using various chemical precursors. Electrochemical performance of materials demonstrates considerable dependence on their chemical prehistory and Li stoichiometry. Increase in duration of the final annealing at 900 °C since 1–12 h results in decreasing capacity values for all x and chemical prehistories. Observed capacity fall is explained by smaller grain size and, therefore, shorter Li diffusion pathways in the samples obtained using short time annealing.     

Electrochemical behavior of polyamides with cyclic disulfide structure and their application to positive active material for lithium secondary battery

Polyamides (DTA-I, DTA-II, and DTA-III) containing cyclic disulfide structure were prepared by condensation between 1,2-dithiane-3,6-dicarboxylic acid (DTA) and alkyl diamine, NH₂–(CH₂)_n–NH₂ (DTA-I; n=4, DTA-II; n=6, DTA-III; n=8) and their application to positive active material for lithium secondary batteries was investigated. Cyclic voltammetry (CV) measurements under slow sweep rate (0.5 mV s⁻¹) with a carbon paste electrode containing the polyamide (DTA-I, DTA-II, or DTA-III) were performed. The results indicated that the polyamides were electroactive in the organic electrolyte solution (propylene carbonate (PC)-1,2-dimethoxyethane (DME), 1:1 by volume containing lithium salt, such as LiClO₄). The responses based on the redox of the disulfide bonds in the polyamide were observed.Test cells, Li/PC-DME (1:1. by volume) with 1 mol dm⁻³ LiClO₄/the polyamide cathode, were constructed and their performance was tested under constant current charge/discharge condition. The average capacity of the test cells with the DTA-III cathode was 64.3 Ah kg⁻¹ of cathode (135 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (2.10 V)). Performance of the cell with linear polyamide containing disulfide bond (–CO–(CH₂)₂–S–S–(CH₂)₂–CONH–(CH₂)₈–NH–, GTA-III) was also investigated and the average capacity was 56.8 Ah kg⁻¹ of cathode (100 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (1.76 V)). Cycle efficiency of the test cell with the DTA-III cathode was higher than that with the GTA-III cathode.     

Electrochemical insertion of lithium and sodium into (MoO2)2P2O7

Insertion of lithium and sodium into phosphate (MoO₂)₂P₂O₇ was investigated electrochemically to determine the usefulness as a possible cathode for ion-transfer secondary batteries. Specific charges of up to 250 mA h g⁻¹ were obtained for A/(MoO₂)₂P₂O₇ (A: Li, Na) cells with liquid organic electrolytes in the first reduction half-cycle at room temperature. Intercalation processes under constant current densities of 0.2 mA cm⁻² were reversible within the range of composition 0.85<x<4.0 for lithium and 0.5<x<3.1 for sodium in A_x(MoO₂)₂P₂O₇ (A: Li, Na), respectively. Structural changes induced by lithium or sodium intercalation were followed by ex situ X-ray diffraction measurements, and the phase change from the crystal to the amorphous was observed in both cases.     

Recent developments and future prospects for lithium rechargeable batteries

Possible future developments of lithium rechargeable batteries are discussed. Lithium ion liquid electrolyte batteries are now well established, with energy densities of up to around 150 Wh kg⁻¹. There are prospects of increases in the energy density to perhaps 200–250 Wh kg⁻¹ by using new cathode materials (lithium nickel cobalt oxide) and light weight construction. High power cells make it possible for these batteries to find new uses, e.g. in military applications. Some new materials could reduce the cost, which might make lithium rechargeable batteries economic for electric vehicles.     

Electrochemical characterization of blend polymer electrolytes based on poly(oligo[oxyethylene]oxyterephthaloyl) for rechargeable lithium metal polymer batteries

Solid polymer electrolytes composed of poly(ethylene oxide)(PEO), poly(oligo[oxyethylene]oxyterephthaloyl) and lithium perchlorate have been prepared and characterized. Addition of poly(oligo[oxyethylene]oxyterephthaloyl) to PEO/LiClO₄ reduced the degree of crystallinity and improved the ambient temperature ionic conductivity. The blend polymer electrolyte containing 40 wt.% of poly(oligo[oxyethylene]oxyterephthaloyl) showed an ionic conductivity of 2.0 × 10⁻⁵ S cm⁻¹ at room temperature and a sufficient electrochemical stability to allow application in the lithium batteries. By using the blend polymer electrolytes, the lithium metal polymer cells composed of lithium anode and LiCoO₂ cathode were assembled and their cycling performances were evaluated at 40 °C.     

Electrochemical performance behavior of combustion-synthesized LiNi0.5Mn0.5O2 lithium-intercalation cathodes

LiNiO₂, partially substituted with manganese in the form of a LiNi_0.5Mn_0.5O₂ compound, has been synthesized by a gelatin assisted combustion method [GAC] method. Highly crystalline LiNi_0.5Mn_0.5O₂ powders with R3m symmetry have been obtained at an optimum temperature of 850 °C, as confirmed by PXRD studies. The presence of cathodic and anodic CV peaks exhibited by the LiNi_0.5Mn_0.5O₂ cathode at 4.4 and 4.3 V revealed the existence of Ni and Mn in their 2+ and 4+ oxidation states, respectively. The synthesized LiNi_0.5Mn_0.5O₂ cathode has been subjected to systematic electrochemical performance evaluation, via capacity tapping at different cut-off voltage limits (3.0–4.2, 3.0–4.4 and 3.0–4.6 V) and the possible extraction of deliverable capacity under different current drains (0.1C, 0.5C, 0.75C and 1C rates). The LiNi_0.5Mn_0.5O₂ cathode exhibited a maximum discharge capacity of 174 mAh g⁻¹ at the 0.1C rate between 3.0 and 4.6 V. However, a slightly decreased capacity of 138 mAh g⁻¹ has been obtained in the 3.0–4.4 V range, when discharged at the 1C rate. On the other hand, extended cycling at the 0.1C rate encountered an acceptable capacity fade in the 3.0–4.4 V range (<10%) for up to 50 cycles.     

Further development of lithium/polycarbon monofluoride envelope cells

Lithium primary cells in a light weight plastic envelope format have been made using carbon monofluoride (CF_x) as cathode material, because previous work showed that this cathode material has the highest energy density in lithium primary batteries. Energy densities of around 650 Wh kg⁻¹ were obtained in an envelope cell. Different electrolytes have been examined for high rate and low temperature performance.     

Electrochemical lithium insertion in TiO2 with the ramsdellite structure

The electrochemical insertion of lithium in the ramsdellite polymorph of titanium dioxide, TiO₂ (R), is studied by electrochemical methods. At room temperature the maximal Li uptake under constant current densities of 0.1, 0.5 and 1.0 mA cm⁻² is 0.85, 0.8 and 0.7 Li/Ti, respectively. Between 2.3 and 1.3 V versus lithium, the specific capacity achieved is as high as 285 A h kg⁻¹ at 0.5 mA cm⁻². This corresponds to 85% of the maximum theoretical capacity (336 A h kg⁻¹), which may be reached by incorporation of one lithium per titanium under equilibrium conditions.     

Structure and performance of porous polymer electrolytes based on P(VDF-HFP) for lithium ion batteries

In order to develop polymer electrolyte for lithium ion batteries, highly porous P(VDF-HFP) membranes were prepared by using phase inversion method, then they were immerged in 1 mol kg⁻¹ solution of LiClO₄-EC/PC(1:1) to form porous polymer electrolytes. Conductivity of the polymer electrolytes was found to be as high as 10⁻³ S cm⁻¹. Structures of the porous membranes were observed with SEM. Porous membranes with different structure, porosity and pore diameter were prepared by changing the processing conditions. There are two kinds of typical structure, one is honeycomb-like (type I), and the other is network-like (type II). Membrane structures were found to be important to the performance of the porous polymer electrolytes. Small pore diameter with narrow distribution is needed to prevent solution leakage and high porosity is needed to achieve high conductivity. The type II membranes can meet the requirements. The model lithium ion batteries made of the resulting porous polymer electrolytes have good cycleablity.     

Effects of addition of TiO2 nanoparticles on mechanical properties and ionic conductivity of solvent-free polymer electrolytes based on porous P(VdF-HFP)/P(EO-EC) membranes

To enhance the performance (i.e., mechanical properties and ionic conductivity) of pore-filling polymer electrolytes, titanium dioxide (TiO₂) nanoparticles are added to both a porous membrane and its included viscous electrolyte, poly(ethylene oxide-co-ethylene carbonate) copolymer (P(EO-EC)). A porous membrane with 10 wt.% TiO₂ shows better performance (e.g., homogeneous distribution, high uptake, and good mechanical properties) than the others studied and is therefore chosen as the matrix to prepare polymer electrolytes. A maximum conductivity of 5.1 × 10⁻⁵ S cm⁻¹ at 25 °C is obtained for a polymer electrolyte containing 1.5 wt.% TiO₂ in a viscous electrolyte, compared with 3.2 × 10⁻⁵ S cm⁻¹ for a polymer electrolyte without TiO₂. The glass transition temperature, T_g is lowered by the addition of TiO₂ (up to 1.5 wt.% in a viscous electrolyte) due to interaction between P(EO-EC) and TiO₂, which weakens the interaction between oxide groups of the P(EO-EC) and lithium cations. The overall results indicate that the sample prepared with 10 wt.% TiO₂ for a porous membrane and 1.5 wt.% TiO₂ for a viscous electrolyte is a promising polymer electrolyte for rechargeable lithium batteries.     

Photocured PEO-based solid polymer electrolyte and its application to lithium–polymer batteries

A solid polymer electrolyte (SPE) based on polyethylene oxide (PEO) is prepared by photocuring of polyethylene glycol acrylates. The conductivity is greatly enhanced by adding low molecular weight poly(ethylene glycol) dimethylether (PEGDME). The maximum conducticity is 5.1×10⁻⁴ S cm⁻¹ at 30°C. These electrolytes display oxidation stability up to 4.5 V against a lithium reference electrode. Reversible electrochemical plating/stripping of lithium is observed on a stainless steel electrode. Li/SPE/LiMn₂O₄ as well as C(Li)/SPE/LiCoO₂ cells have been fabricated and tested to demonstrate the applicability of the resulting polymer electrolytes in lithium–polymer batteries.     

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.     

Preparation of LiMn2O4 at the low temperature of 250 °C using eutectic self-mixing method

Spinel LiMn₂O₄ as a cathode material for lithium rechargeable batteries is prepared at the low temperature of 250 °C without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on heating at 250 °C. The prepared material exhibits the initial discharge capacity of 85.5 mAh g⁻¹ and the discharge capacity retention of 91.5% after 50 cycles.