•Fe3+ Impurities free LiFePO4 has been synthesized via hydrothermal method using ferrocene carboxylic acid as an iron source.•Electron paramagnetic resonance spectroscopy has been used for determination of Fe3+ concentration in LiFePO4.•The LiFePO4 electrode demonstrates good electrochemical performance.The iron precursor of lithium iron phosphate (LiFePO4) is highly prone to oxidation to Fe3+ during the hydrothermal synthesis. The Fe3+ impurities in LiFePO4 restrict the conduction path of Li+ ions in LiFePO4, which negatively affect the cell performance. In this paper, we report that ferrocenecarboxylic acid possessing an extremely stable Fe2+ species and as carbon source has been used successfully to suppress Fe3+ impurities in LiFePO4. The X-ray diffraction results reveal that Li2CO3 first reacts with (NH4)2HPO4 to form Li3PO4 at low temperatures, which above 160 °C further reacts with ferrocenecarboxylic acid to give LiFePO4. The infrared spectroscopy, nuclear magnetic resonance, mass spectrometry, and elemental analysis results show that the carbon sources during calcination of LiFePO4 are derived from polymers through sequential [4 + 2] cycloaddition reactions of cyclopentadiene and 1,3-cyclopentadiene-1-carboxylic acid during decomposition of ferrocenecarboxylic acid. The electron paramagnetic resonance results show that the percentage of Fe3+ in the synthesized LiFePO4 is as low as 0.5 mol%. A plausible reaction mechanism for the hydrothermal synthesis of LiFePO4 is also proposed. The as-synthesized LiFePO4 shows an orthorhombic olivine with a discharge capacity of 158 mAh g−1 at a discharge rate of 0.1C. The cell also shows excellent C-rate and cycle-life performances.Download high-res image (165KB)Download full-size image

Nitroxide polymer brush grafted on superparamagnetic nanoparticles has been synthesized. Using the brush as a catalyst, the conversion by catalytic oxidation of alcohols to aldehydes and ketones is more than 99%. The catalyst can be easily recovered by applying a magnetic field. Furthermore, the reused catalyst still maintain high performance in catalytic oxidation.

The development of electrolytes capable of performing at a high voltage (>5 V) is essential for the advancement of lithium-ion batteries. In the present work, we have investigated a dinitrile–mononitrile-based electrolyte system that can offer electrochemical stability up to 5.5 V at room temperature. The electrolytes consist of 1.0 M lithium bis(trifluoromethane)sulfonamide in various volume proportions of glutaronitrile, a dinitrile, and butyronitrile, a mononitrile (10/0; 8/2; 6/4; 4/6; 2/8; 10/0). The ionic conductivity of the electrolytes was found to be 3.1 × 10–3–10.6 × 10–3 S cm–1 at 30 °C, comparable with commercially used carbonate-based electrolytes. However, butyronitrile reacts with Li metal to give 3-amino-2-ethylhex-2-ene-nitrile, 2,6-dipropyl-5-ethylpyrimidin-4-amine, and oligomers/polymers. These compounds have been characterized by nuclear magnetic resonance techniques, and based on these findings, a plausible mechanism of reactivity of mononitriles toward Li metal has been proposed. Finally, 5 wt % of vinylene carbonate is added to the glutaronitrile/butyronitrile (6/4 ratio) system to inhibit the reductive decomposition of butyronitrile. The resultant electrolyte system is used in the assembly of several coin cells consisting of a LiFePO4 composite cathode and a Li metal anode. The cells perform up to 3 C charge/discharge rate with reasonably good discharge capacity and also display a cycle life of more than 100 cycles at a 0.5 C rate with capacity retention above 95% at room temperature.

A poly(2,2,6,6-tetramethylpiperidin-1-oxy-4-yl methacrylate)/carbon-nanotube-array (PTMA/CNT-array) electrode was used as a cathode to improve the high-rate charge/discharge performance in organic radical batteries. Scanning electron microscopy observations showed that the PTMA/CNT-array electrode provides continuous conduction paths for electrons, and its electrochemical behaviours were investigated using cyclic voltammetry, charge/discharge tests, and AC impedance measurements. The results indicated that the PTMA/CNT-array electrode exhibits a lower electron-transfer resistance between CNTs and either the current collector or CNTs compared with conventional PTMA/suspended-CNT composite electrodes, enhancing the C-rate performance of batteries.

•The SEI formed on MCMB in the PC-based electrolyte without additives was characterized.•The PC-based SEI dissolves in the electrolyte at 30 °C.•The dissolution of the SEI affects the electrochemical performance.•The chemical composition of the SEI was investigated.The effects of temperature on the dissolution of solid electrolyte interface (SEI) films in the propylene carbonate (PC)-based electrolyte are investigated. The SEI films on the mesocarbon microbeads (MCMB) electrode of the Li|1.0 M LiPF6-PC/DEC (= 7/3, v/v)|MCMB cell are characterized by cyclic voltammetry, scanning electron microscopy (SEM), AC impedance, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The SEM and electrochemical results show that the MCMB electrode cannot undergo the lithiation and delithiation process at 30 °C due to the co-intercalation of PC and the exfoliation of MCMB. By contrast, the Li∥MCMB cell can be successfully discharged and charged at 0 °C because a PC-based SEI film forms on MCMB. The energy capacity of the MCMB electrode is 281.3 mAh g−1 at 0.2 C. However, the SEI film dissolves in the PC-based electrolyte as the temperature is increased to 30 °C. The results of Raman spectroscopy and XPS also confirm that the composition of the PC-based SEI formed at 0 °C consists of LiF, LixPFy, LixPOyFz, ROLi, and ROCO2Li.

Lithium iron phosphate (LiFePO4) is synthesized by a hydrothermal process using pyrrole as an efficient reducing agent and a subsequent calcination. Observations through a scanning electron microscope and a transmission electron microscope (TEM) show that LiFePO4 has a diameter and length of 500 nm and 3 μm, respectively. The results of TEM and X-ray diffraction confirm that the structure of LiFePO4 is orthorhombic olivine. Raman and X-ray photoelectron spectroscopy results indicate that Fe3+ oxidized from reactant Fe2+ by air reacts with pyrrole, generating polypyrrole (PPy), and reduces to Fe2+. PPy that is generated can also serve as a carbon source in the subsequent calcination. In addition, the electrochemical measurement results show that the energy capacity of calcined LiFePO4/PPy is 153 mAh g−1 at 0.2 C. Calcined LiFePO4/PPy offers promising cycle-life performance in lithium-ion batteries.Highlights► Pyrrole is used as efficient reducing agent for hydrothermal synthesis of LiFePO4. ► Addition of pyrrole reduces Fe3+ to Fe2+. ► Pyrrole polymerizes to polypyrrole, creating a carbon source. ► LiFePO4 has high electrochemical performance in lithium-ion batteries.

Nitroxide polymer brushes for thin-film electrodes for organic radical batteries are synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP). Patterned nitroxide polymer brush thin-film electrodes are fabricated by microcontact printing. The thickness of the polymer brushes is proportional to the polymerization time of SI-ATRP. The results of cyclic voltammetry and AC impedance indicate that when the polymer brush is thicker than 55 nm, the poly(2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMPM) segment at the bottom of the brush is not sufficiently oxidized to yield a nitroxide polymer brush during a 10 min oxidation time. Electrochemical and X-ray photoelectron spectroscopy results also show that an increase in the oxidation time could oxidize the PTMPM segment at the bottom of the brush but results in over-oxidation of the brush at the top, which decreases the energy capacity of the polymer brush. Moreover, the energy capacity of the polymer brush electrode for organic radical batteries is determined to be approximately 94.0 mA h g−1 at a discharge rate of 20 C; its cycle-life performance exhibits 97.3% retention after 100 cycles. Atomic force microscopy results also confirm that after 100 cycles the surface morphology of the polymer brush electrodes does not show obvious changes, indicating that the polymer brush resists dissolution of polymers into electrolytes.

Synthesis of 2,5-poly(3-[1-ethyl-2-(2-bromoisobutyrate)]thiophene)-graft-poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PEBBT-g-PTMA) and its electrochemical properties in organic radical batteries have been reported. The polythiophene-based macroinitiator PEBBT, synthesized from 3-[1-ethyl-2-(2-bromoisobutyrate)]thiophene, grafts with poly(2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMPM) to yield PEBBT-g-PTMPM via atom transfer radical polymerization (ATRP). The conditions for ATRP of 2,2,6,6-tetramethylpiperidin-4-yl methacrylate (TMPM) are optimized by examining a series of model polymerizations. PEBBT-g-PTMPM is oxidized by m-chloroperoxybenzoic acid to yield PEBBT-g-PTMA with a relatively high molecular weight (Mn = 483300) that prevents the dissolution of the polymer into electrolytes. PEBBT-g-PTMA has been evaluated as a cathode-active material in a rechargeable organic radical battery. The result of cyclic voltammetry shows a redox couple at approximately 3.6 V (vs. Li/Li+). Furthermore, the cell performance shows that the organic radical battery has good electrochemical stability and good cyclability.

The electrochemical behavior of a poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA) cathode in organic radical batteries with lithium bis(trifluoromethylsulfonyl)imide in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (LiTFSI/BMPTFSI) ionic liquid electrolytes is investigated. The ionic liquid electrolytes containing a high concentration of the LiTFSI salt have a high polarity, preventing the dissolution of the polyvinylidene fluoride binder and PTMA in the electrolytes. The results of cyclic voltammetry and AC impedance indicate that an increase in the LiTFSI concentration results in a decrease in the impedance of the lithium electrode, which affects the C-rate performance of batteries. The discharge capacity of the PTMA composite electrode in a 0.6 m LiTFSI/BMPTFSI electrolyte is 92.9 mAh g−1 at 1 C; its C-rate performance exhibits a capacity retention, 100 C/1 C, of 88.3%. Moreover, the battery with the 0.6-m LiTFSI/BMPTFSI electrolyte has very good cycle-life performance.Highlights► Pyrrolidinium ionic liquid was used as an electrolyte in an organic radical battery. ► Addition of lithium salt suppresses the dissolution of the polyvinylidene fluoride binder into the electrolyte. ► Addition of lithium salt decreases the resistance of the solid electrolyte interface film. ► Cells with the pyrrolidinium ionic liquid electrolytes demonstrate excellent electrochemical performance.

Nitroxide polymer brushes were covalently patterned on flexible conducting substrates via surface-initiated atom transfer radical polymerization and microcontact printing. As a cathode of organic radical batteries, the nitroxide polymer brushes prevent the nitroxide polymer from dissolving into electrolyte solvents, which improves the cycle-life performance of batteries.

Nitroxide polymer brushes grafted on silica nanoparticles as binder-free cathodes for organic radical batteries have been investigated. Scanning electron microscopy, transmission electron microscopy, infrared spectroscopy and electron spin resonance confirm that the nitroxide polymer brushes are successfully grafted onto silica nanoparticles via surface-initiated atom transfer radical polymerization. The thermogravimetric analysis results indicate that the onset decomposition temperature of these nitroxide polymer brushes is found to be ca. 201 °C. The grafting density of the nitroxide polymer brushes grafted on silica nanoparticles is 0.74–1.01 chains nm−2. The results of the electrochemical quartz crystal microbalance indicate that the non-crosslinking nitroxide polymer brushes prevent the polymer from dissolving into organic electrolytes. Furthermore, the electrochemical results show that the discharge capacity of the polymer brushes is 84.9–111.1 mAh g−1 at 10 C and the cells with the nitroxide polymer brush electrodes have a very good cycle-life performance of 96.3% retention after 300 cycles.Graphical abstractHighlights► Nitroxide polymer brushes on silica nanoparticles as cathodes were prepared by ATRP. ► The nitroxide polymer brush prevents the polymer from dissolving into electrolytes. ► The nitroxide polymer brushes serve as bind-free cathode materials. ► The nitroxide polymer brushes demonstrate excellent electrochemical performances.

The deposition of Al2O3 on LiCoO2 electrodes using a low-temperature atomic layer deposition has been investigated. Scanning electron microscopy confirms that Al2O3 films can be homogeneously deposited on LiCoO2 particles of porous electrodes at 120 °C. The results of X-ray photoelectron spectroscopy show that the Al2O3 preferentially deposits on the LiCoO2. Furthermore, the results of cycling stability tests show that the cells with Al2O3-coated LiCoO2 electrodes have enhanced performance.

Highly hydroxylated barium titanate (BaTiO3) nanoparticles have been prepared via an easy and gentle approach which oxidizes BaTiO3 nanoparticles using an aqueous solution of hydrogen peroxide (H2O2). The hydroxylated BaTiO3 surface reacts with sodium oleate (SOA) to form oleophilic layers that greatly enhance the dispersion of BaTiO3 nanoparticles in organic solvents such as tetrahydrofuran, toluene, and n-octane. The results of Fourier transform infrared spectroscopy confirmed that the major functional groups on the surface of H2O2-treated BaTiO3 nanoparticles are hydroxyl groups which are chemically active, favoring chemical bonding with SOA. The results of transmission electron microscopy of SOA-modified BaTiO3 nanoparticles suggested that the oleate molecules were bonded to the surfaces of nanoparticles and formed a homogeneous layer having a thickness of about 2 nm. Furthermore, the improved dispersion capability of the modified BaTiO3 nanoparticles in organic solvents was verified through analytic results of its settling and rheological behaviors.The surfaces of BaTiO3 nanoparticles were highly hydroxylated by H2O2(aq). The hydroxylated BaTiO3 surface reacted with sodium oleate to form oleophilic layers to greatly enhance its dispersion in organic solvents.

Nitroxide polymer brushes were covalently patterned on flexible conducting substrates via surface-initiated atom transfer radical polymerization and microcontact printing. As a cathode of organic radical batteries, the nitroxide polymer brushes prevent the nitroxide polymer from dissolving into electrolyte solvents, which improves the cycle-life performance of batteries.

Nitroxide polymer brushes for thin-film electrodes for organic radical batteries are synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP). Patterned nitroxide polymer brush thin-film electrodes are fabricated by microcontact printing. The thickness of the polymer brushes is proportional to the polymerization time of SI-ATRP. The results of cyclic voltammetry and AC impedance indicate that when the polymer brush is thicker than 55 nm, the poly(2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMPM) segment at the bottom of the brush is not sufficiently oxidized to yield a nitroxide polymer brush during a 10 min oxidation time. Electrochemical and X-ray photoelectron spectroscopy results also show that an increase in the oxidation time could oxidize the PTMPM segment at the bottom of the brush but results in over-oxidation of the brush at the top, which decreases the energy capacity of the polymer brush. Moreover, the energy capacity of the polymer brush electrode for organic radical batteries is determined to be approximately 94.0 mA h g−1 at a discharge rate of 20 C; its cycle-life performance exhibits 97.3% retention after 100 cycles. Atomic force microscopy results also confirm that after 100 cycles the surface morphology of the polymer brush electrodes does not show obvious changes, indicating that the polymer brush resists dissolution of polymers into electrolytes.