Electrochemical properties of carbon-coated Si/B composite anode for lithium ion batteries

Carbon-coated Si and Si/B composite powders prepared by hydrocarbon gas (argon + 10 mol% propylene) pyrolysis were investigated as the anodes for lithium-ion batteries. Carbon-coated silicon anode demonstrated the first discharge and charge capacity as 1568 mAh g⁻¹ and 1242 mAh g⁻¹, respectively, with good capacity retention for 10 cycles. The capacity fading rate of carbon-coated Si/B composite anode decreased as the amounts of boron increased. In addition, the cycle life of carbon-coated Si/B/graphite composite anode has been significantly improved by using sodium carboxymethyl cellulose (NaCMC) and styrene butadiene rubber (SBR)/NaCMC mixture binders compared to the poly(vinylidene fluoride, PVdF) binder. A reversible capacity of about 550 mAh g⁻¹ has been achieved at 0.05 mAm g⁻¹ rate and its capacity could be maintained up to 450 mAh g⁻¹ at high rate of 0.2 mAm g⁻¹ even after 30 cycles. The improvement of the cycling performance is attributed to the lower interfacial resistance due to good electric contact between silicon particles and copper substrate.     

Catalytically graphitized glass-like carbon examined as anode for lithium-ion cell performing at high charge/discharge rates

The influence of a long-time heat treatment of hard carbon in the presence of iron catalyst on its structural properties and electrochemical performance is concerned in terms of potential application as anode material for lithium-ion cell. Glass-like carbon spheres obtained by carbonization of phenol resin were catalytically graphitized by heat treatment at temperature 1000 °C in argon atmosphere for 20 h and 100 h. After this process iron was completely removed from the product of reaction. The original carbon was entirely useless as anode for Li-ion cell because of its extremely poor reversible capacity (54 mAh g⁻¹). Due to heat treatment composite materials consisting of microcrystalline graphite admixed with turbostratic carbon were produced. Modified carbons were tested as anode materials using gradually increasing current density. Based on electrochemical measurements a mixed intercalation/insertion mechanism for storage of lithium ions was concluded. Discharge capacity of carbon heat treated for 100 h attained value of 276 mAh g⁻¹ and its reversible capacity appeared to be better than that of flaky graphite upon discharging at current density in the range 50-250 mA g⁻¹.     

Investigation on porous MnO microsphere anode for lithium ion batteries

MnO microspheres with and without carbon coating are prepared as anode materials for lithium ion batteries. The MnO microsphere material shows a reversible capacity of 800 mAh g⁻¹ and an initial efficiency of 71%. It can deliver 600 mAh g⁻¹ at a rate of 400 mA g⁻¹. Results of Mn K-edge X-ray absorption near-edge structure (XANES) spectra and extended X-ray absorption fine structure (EXAFS) confirm further the conversion reaction mechanism, indicate that pristine MnO is reduced to Mn⁰ after discharging to 0 V and part of reduced Mn⁰ is not oxidized to Mn²⁺ after charging to 3 V. This explains the origin of the initial irreversible capacity loss partially. The quasi open circuit voltage and the relationship between the current density and the overpotential are investigated. Both indicate that there is a significant voltage difference between the charging and discharging profiles even when the current density decreases to zero.     

Electrochemical properties of Si–Zn–C composite as an anode material for lithium-ion batteries

A Si–Zn–C composite material is prepared by mechanical ball-milling and investigated as an anode material for lithium-ion batteries. Electrochemical tests show that the first charge and discharge capacities are approximately 852 and 607 mAh g⁻¹, respectively, and that 91% of the initial discharge capacity of 607 mAh g⁻¹ can be maintained for up to 40 cycles. This improved cycling performance is attributed to the use of the third element Zn. Li₂ZnSi is partially formed at the interface between Si and Zn and graphite to provide superior cycling performance compared with that of the binary system.     

Spherical silicon/graphite/carbon composites as anode material for lithium-ion batteries

A spherical nanostructured Si/graphite/carbon composite is synthesized by pelletizing a mixture of nano-Si/graphite/petroleum pitch powders, followed by heat treatment at 1000 °C under an argon atmosphere. The structure of the composite sphere is examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX). The resultant composite sphere consists of nanosized silicon and flaked graphite embedded in a carbon matrix pyrolyzed from petroleum pitch, in which the flaked graphite sheets are concentrically distributed in a parallel orientation. The composite material exhibits good electrochemical properties, a high reversible specific capacity of ∼700 mAh g⁻¹, a high coulombic efficiency of 86% on the first cycle, and a stable capacity retention. The enhanced electrochemical performance is attributed to the structural stability of the composite sphere during the charging–discharging process.     

MnO powder as anode active materials for lithium ion batteries

MnO powder materials are investigated as anode active materials for Li-ion batteries. Lithium is stored reversibly in MnO through conversion reaction and interfacial charging mechanism, according to the results of ex situ XRD, TEM and galvanostatic intermittent titration technique. A layer of the solid electrolyte interphase with a thickness of 20-60 nm is covered on MnO particles after full insertion. MnO powder materials show reversible capacity of 650 mAh g⁻¹ with average charging voltage of 1.2 V. It can deliver 400 mAh g⁻¹ at a rate of 400 mA g⁻¹. The cyclic performance of MnO is improved significantly after decreasing particle size and coating with a layer of carbon. Among observed transition metal oxides, MnO shows relatively lower voltage hysteresis (<0.7 V) between the discharging and the charging curves at 0.05 C. In addition to its environmental benign feature and high density (5.43 g cm⁻³), MnO seems a promising high capacity anode material for Li-ion batteries among transition metal oxides. However, the initial columbic efficiency is less than 65% and the voltage hysteresis is still too high. The origins of them are discussed.     

Low temperature behaviour of TiO2 rutile as negative electrode material for lithium-ion batteries

High surface nanosized rutile TiO₂ is prepared via a sol-gel method from an ethylene glycol-based titanium-precursor in the presence of a non-ionic surfactant, at pH 0. Its electrochemical behaviour has been investigated at low temperature using two different potential windows. Typically, the potential window of the rutile system is 1-3 V but the use of an enlarged potential window (0.1-3 V), leads to an excellent reversible capacity of 341 mAh g⁻¹ which is comparable to graphite anodes. The electrochemical performance was investigated by cyclic voltammetry and galvanostatic techniques at temperatures ranging from −40 to 20 °C. Nanosized TiO₂ exhibits excellent rate capability (341 mAh g⁻¹ at 20 °C, 197 mAh g⁻¹ at −10 °C, 138 mAh g⁻¹ at −20 °C, and 77 mAh g⁻¹ at −40 °C at a C/5 rate) and good cycling stability. The superior low-temperature electrochemical performance of nanosized rutile TiO₂ may make it a promising candidate as lithium-ion battery material.     

Surface-modified meso-carbon microbeads anode for dry polymer lithium-ion batteries

A high-anode performance for dry polymer lithium-ion batteries was obtained in the surface-modified meso-carbon microbeads (MCMB). MCMB and polyvinylchloride (PVC) mixture was heated at 700 °C for 6 h under inert atmosphere. By this treatment, the surface of MCMB is covered with low-crystalline carbon material derived from PVC pyrolysis. The surface-modified MCMB electrode applied to dry polymer electrolytes shows a reversible capacity of 300 mAh g⁻¹, which is comparable to those obtained in the liquid electrolyte systems.     

High voltage spinel cathode materials for high energy density and high rate capability Li ion rechargeable batteries

We have synthesized LiMn_1.5Ni_0.4Cr_0.1O₄ cathode material for high energy density Li ion rechargeable batteries using sol-gel method. The synthesized materials were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, cyclic voltammetry and charge-discharge characteristics. It was found that phase pure materials were obtained an annealing temperature of 875 °C for 15 h. The maximum discharge capacity at a constant charge-discharge current rate 1C, 0.5C, and 0.2C were found to be about 99 mAh g⁻¹, 110 mAh g⁻¹, and 131 mAh g⁻¹, respectively. The capacity retentions after 50 charge-discharge cycles were found to be about 99%, 97%, and 97.3% at discharge current rates of 0.2C, 0.5C, and 1C. The stable electrochemical behavior of the above cathode material even at high C rate, showed that it could be used for high energy density and high rate capability Li ion rechargeable batteries.     

Cathode performance of LiMnPO4/C nanocomposites prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment

LiMnPO₄/C nanocomposites could be prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment in the range of spray pyrolysis temperature from 200 to 500 °C. The ordered LiMnPO₄ olivine structure without any impurity phase could be identified by X-ray diffraction analysis for all samples. It could be also confirmed from scanning electron microscopy and transmission electron microscopy observations that the final samples were the LiMnPO₄/C nanocomposites with approximately 100 nm in primary particles size. The LiMnPO₄/C nanocomposite samples were used as cathode active materials for lithium batteries, and the electrochemical tests were carried out for the cell Li|1 M LiPF₆ in EC:DMC = 1:1|LiMnPO₄/C at various charge/discharge rates in three charge modes. As a result, the final sample which was synthesized at 300 °C by spray pyrolysis showed the best electrochemical performance due to the largest specific surface area, the smallest primary particle size and a well distribution of carbon. At galvanostatic charge/discharge rates of 0.05 C, the cell delivered first discharge capacities of 123 and 165 mAh g⁻¹ in correspondence to charge cutoff voltages of 4.4 and 5.0 V, respectively. Furthermore, in a constant current-constant voltage charge mode at 4.4 V, the cells also exhibited initial discharge capacities of 147 mAh g⁻¹ at 0.05 C, 145 mAh g⁻¹ at 0.1 C, 123 mAh g⁻¹ at 1 C and 65 mAh g⁻¹ at 10 C. Moreover, the cells showed fair good cycleability over 100 cycles.     

Lithium-ion batteries based on carbon–silicon–graphite composite anodes

The paper is devoted to the development of lithium-ion battery grade negative electrode active materials with higher reversible capacity than that offered by conventional graphite. The authors report on results of their experiments as related to the electrochemical performance of silicon-based materials for lithium-ion batteries. A commercial grade of spherically shaped natural graphite (FormulaBT™ SLA1025) was modified in a number of different ways with nano-sized silicon. The reversible capacity of SLA1025 modified by 9.2 wt% of the nano-sized amorphous silicon was seen to be as high as 590 mAh g⁻¹. The irreversible capacity loss with this compound was 20%. Lithium-ion batteries using such material were observed to display sharp capacity decay during prolonged cycling. In contrast, the reversible capacity of another experimental grade, the SLA1025 modified by 7.9 wt% of the carbon-coated Si was as high as 604 mAh g⁻¹. The irreversible capacity loss with this material was as low as 8.1%. This grade, also, was seen to display much better cycling performance than the baseline natural graphite.     

High-rate discharge properties of nickel hydroxide/carbon composite as positive electrode for Ni/MH batteries

A chemical co-precipitation method was attempted to synthesize nickel hydroxide/carbon composite material for high-power Ni/MH batteries. The XRD analysis showed that there were a large amount of defects among the crystal lattice of the Ni(OH)₂/C composite, and the SEM investigation revealed that the as-synthesized spherical particles were composed of hundreds of nanometer crystals with a unique three-dimensional petal shape. Compared with pure Ni(OH)₂, the Ni(OH)₂/C composite showed improved electrochemical properties such as superior cycling stability, higher discharge capacity and higher mean voltage of discharge under high-rate discharge conditions, the discharge capacity and the mean discharge voltage of the Ni(OH)₂/C composite were about 281 mAh g⁻¹ and 0.303 V (vs. Hg/HgO) at 1 C-rate, 273 mAh g⁻¹ and 0.296 V at 5 C-rate, 250 mAh g⁻¹ and 0.292 V at 10 C-rate, respectively. The cyclic voltammetry (CV) tests showed that the Ni(OH)₂/C composite exhibited good electrochemical reversibility and the formation of γ-NiOOH during the charge–discharge processes was prevented. The existence of carbon in the Ni(OH)₂/C composite contributed great effect on the improvement of high-rate discharge performance.     

A new process of preparing composite microstructure anode for lithium ion batteries

A composite material anode for lithium ion batteries (LIB) consisted of electrodeposited Sn–Sb alloy dispersing in a conductive micro-porous carbon membrane coated on Cu current collector was investigated. The composite material was obtained by directly electrodepositing Sn–Sb alloy on the micro-porous membrane electrode via micro-pores in it, which was prepared by casting a polyacrylonitrile (PAN) solution containing polyethylene glycol (PEG) on a copper foil and then immersing the copper foil into de-ionized water to perform phase inversion, following by heat-treatment. SEM examinations showed that the composite material consisted of isolated pillar-like structure SnSb electrodeposited on Cu current collector dispersing in a conductive micro-porous carbon membrane deriving from pyrolysis of PAN. Constant current charge and discharge tests using the composite anode showed stable coulombic efficiency and desirable cyclability. The reversible discharging capacity was 339.5 mAh g⁻¹after 50 cycles, corresponding to 78.6% of the discharge capacity retention.     

Reduced graphene oxide/tin oxide composite as an enhanced anode material for lithium ion batteries prepared by homogenous coprecipitation

Reduced graphene oxide/tin oxide composite is prepared by homogenous coprecipitation. Characterizations show that tin oxide particles are anchored uniformly on the surface of reduced graphene oxide platelets. As an anode material for Li ion batteries, it has 2140 mAh g⁻¹ and 1080 mAh g⁻¹ capacities for the first discharge and charge, respectively, which is more than the theoretical capacity of tin oxide, and has good capacity retention with a capacity of 649 mAh g⁻¹ after 30 cycles. The simple synthesis method can be readily adapted to prepare other composites containing reduced graphene oxide as a conducting additive that, in addition to supporting metal oxide nanoparticles, can also provide additional Li binding sites to, perhaps, further enhance capacity.     

Vertically aligned carbon nanotube electrodes for lithium-ion batteries

As portable electronics become more advanced and alternative energy demands become more prevalent, the development of advanced energy storage technologies is becoming ever more critical in today's society. In order to develop higher power and energy density batteries, innovative electrode materials that provide increased storage capacity, greater rate capabilities, and good cyclability must be developed. Nanostructured materials are gaining increased attention because of their potential to mitigate current electrode limitations. Here we report on the use of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) as the active electrode material in lithium-ion batteries. At low specific currents, these VA-MWNTs have shown high reversible specific capacities (up to 782 mAh g⁻¹ at 57 mA g⁻¹). This value is twice that of the theoretical maximum for graphite and ten times more than their non-aligned equivalent. Interestingly, at very high discharge rates, the VA-MWNT electrodes retain a moderate specific capacity due to their aligned nature (166 mAh g⁻¹ at 26 A g⁻¹). These results suggest that VA-MWNTs are good candidates for lithium-ion battery electrodes which require high rate capability and capacity.     

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.     

Significant effects of poly(3,4-ethylenedioxythiophene) additive on redox responses of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) cathode for rechargeable Li batteries

Redox behaviors of the poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM)-coated electrodes composited with carbon black (CB) or poly(3,4-ethylenedioxy-thiophene) (PEDOT) are presented. Effects of PEDOT additive on the redox activity of PDBM were investigated to apply their composite materials as candidates of cathodes for rechargeable lithium batteries. The film having a PEDOT/PDBM with weight ratio of 1/1 shows a gravimetric capacity of 129 mAh g⁻¹ (corresponding to 188 mAh g⁻¹ for PDBM and 70 mAh g⁻¹ for PEDOT). The highest energy density observed was 140 mAh g⁻¹ (406 mWh g⁻¹) for the composite cathode. Good cycle-ability over 100 cycles was attained with a PEDOT/PDBM composite cathode.     

Surface-modified maghemite as the cathode material for lithium batteries

The inorganic–organic hybrid maghemite (γ-Fe₂O₃)/polypyrrole (PPy) was synthesized and evaluated as cathode-active material for room temperature lithium batteries. The nanometer-sized core–shell structure of the hybrid consisting of the maghemite core with surface modified by PPy was evidenced from the morphological examination. The cathode fabricated with the as-prepared hybrid material delivered an initial discharge capacity of 233 mAh g⁻¹ and a reversible capacity of ∼62 mAh g⁻¹ after 50 charge–discharge cycles. A much higher performance with an initial discharge capacity of 378 mAh g⁻¹ and a reversible capacity of ∼100 mAh g⁻¹ was achieved with the cathode based on the segregated active material, which was obtained by subjecting the as-prepared hybrid material to an additional ball-milling process. The study demonstrates the promising lithium insertion characteristics of the nanometer-sized core–shell maghemite/PPy particles prepared under optimized conditions for application in secondary batteries.     

Temperature effect on the graphite exfoliation in propylene carbonate based electrolytes

Graphite exfoliation at a low potential has long been an issue for lithium-ion cells using a propylene carbonate (PC) based electrolyte. Two different mechanisms have been proposed in literature to explain this structural degradation. In this study, the initial lithium intercalation temperature is found to have a great impact on the extent of the graphite exfoliation. At an elevated temperature, the exfoliation can be largely suppressed and the irreversible capacity loss is reduced substantially. After the initial cycling at 50 °C, the graphite anode can be cycled in a PC-based electrolyte at room temperature without the exfoliation problem. It is also discovered that such a graphite anode gives rise to a specific capacity of over 372 mAh g⁻¹ at 50 °C and a room temperature capacity higher than that of a graphite anode with the initial lithium intercalation at room temperature. This finding sheds a new light on the exfoliation mechanism. It may lead to a simple cycling procedure that allows us to make rechargeable lithium-ion batteries with better safety and higher capacity.     

Boron doped lithium trivanadate as a cathode material for an enhanced rechargeable lithium ion batteries

Boron was doped into lithium trivanadate through an aqueous reaction process followed by heating at 100 °C. The B-LiV₃O₈ materials as a cathode in lithium batteries exhibits a specific discharge capacity of 269.4 mAh g⁻¹ at first cycle and remains 232.5 mAh g⁻¹ at cycle 100, at a current density of 150 mAh g⁻¹ in the voltage range of 1.8–4.0 V. The B-LiV₃O₈ materials show excellent stability, with the retention of 86.30% after 100 cycles. These result values are higher than those previous reports indicating B-LiV₃O₈ prepared by our synthesis method is a promising candidate as cathode material for rechargeable lithium batteries. The enhanced discharge capacities and their stabilities indicate that boron atoms promote lithium transferring and intercalating/deintercalating during the electrochemical processes and improve the electrochemical performance of LiV₃O₈ cathode.