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Li metal is considered the ultimate electrode for lithium-ion batteries due to its high specific capacity (3860 mAh g–1) and density (0.534 g cm–3). Despite these advantages, the practical use of L...

Recently, great advances of the Li-S battery technology have enabled its penetration as the power source of mid- and large-sized devices, which require high energy and power density that cannot be achieved with Li-ion batteries. While the most successful Li-S battery operation is enabled by the tailoring of the sulfur composite cathode composite structure, the binder system has recently been considered as another important factor. We study the structural and electrochemical performance of sulfur cathodes prepared with two different binders. Enhanced battery performance is observed in the SBR/CMC-based electrode and its origin is scrutinized.

Li4Ti5O12 (LTO)-coated graphite anode materials for lithium-ion batteries with superior rate-capability and cycling performance were prepared by simple ball-milling in a short time. LTO particles, uniformly coated on the surface of graphite active materials, improved the kinetics and stability on the surface of graphite particles on the basis of their high Li-ion diffusivity and structural stability. As a result, the LTO-coated graphite, which was ball-milled for 5 min, presented a high initial discharge capacity (324 mAh g−1 at 0.2 C), superior rate-capability (>260 mAh g−1 at 5 C), and excellent cycling performance (∼94% after 100 cycles at 0.2 C).

A Na0.7MnO2/C composite cathode material is synthesized by simple and costeffective two-step heat treatment for an improvement in the rate capability of Na0.7MnO2. The first heat treatment is to synthesize Na0.7MnO2, and the second one is a low temperature annealing at 350 °C for 1 h in air, which is necessary to suppress an interfacial reaction between the Na0.7MnO2 and C in the synthesis process of Na0.7MnO2/C composite. Structural analyses by XRD and XPS reveal that the Na0.7MnO2/C shows the same structural properties as that of the pristine Na0.7MnO2, and hence they exhibit the same initial discharge capacity of 175 mAh g−1 at 20 mA g−1. At a current density of 400 mA g−1, the discharge capacity of Na0.7MnO2 reduces to 50 mAh g−1 (28% of the initial discharge capacity), whereas that of Na0.7MnO2/C reduces to 108 mAh g−1 (61% of the initial discharge capacity). The enhanced rate capability of the Na0.7MnO2/C is attributed to the conductive carbon layer formed on the surface of Na0.7MnO2 particles, enabling the facile transport of electrons from the current collector to the surface of the Na0.7MnO2 particles.

Sn-Co alloy and Sn-Co/C composite are fabricated on the nodule-type Cu substrate by co-electrodeposition process using the pulse current in the pyrophosphate bath, and then their cycling performances are examined. To modify the surface property of carbon (acetylene black) particles and improve the dispersion of agglomerated carbon particles, CTAB (Cetrimonium bromide (C16H33)N(CH3)3Br) as a cationic surfactant is added into the electrodeposition bath.10.1007/s13391-016-6077-2 By addition of the CTAB, the amount of the carbon content in the Sn-Co/C composite is increased, and also the carbon particles are uniformly distributed in the Sn-Co electrodeposit. The Sn0.6Co0.4 alloy and (Sn0.6Co0.4)0.71/C0.29 composite are obtained after annealing as the final products. The (Sn0.6Co0.4)0.71/C0.29 composite anode exhibits better the capacity retention than the Sn0.6Co0.4 alloy anode due primarily to the role of the well-dispersed carbon particles as the second buffer phase and electrical conductive path in the Sn-Co/C composite during cycling.

Hollow carbon nanospheres as potential cathode materials for lithium-sulfur (Li-S) batteries were successfully synthesized using a metathesis reaction between sodium azide and halogen polymer. The reaction was driven by thermal heat from the exothermic recombination of Na+ and Cl− (or F−) ions into NaCl (or NaF) salts. The result was an increase of the overall system temperature up to 1320–1750 °C followed by the simultaneous formation of sodium halide-carbon core–shell nanoparticles. Therefore, hollow carbon nanospheres with diameter and shell thickness of ∼50–500 nm and ∼10–50 nm, respectively, were produced after water washing of the reaction product. The composite cathode materials for Li-S batteries were manufactured by infiltrating sulfur into the hollow core of nanospheres. The electrochemical cycling showed discharge capacity of ∼700 mAh g−1 (after 100 cycles) at 0.5 C current rate which is more than ∼2.4 times larger than that for the sulfur/carbon black composites prepared by the same technique. The enhancement of battery performance was attributed to the well-organized and unique 3D structure of hollow carbon, enabling better utilization of sulfur.

Lithium (Li) metal is the most attractive anode material for batteries because of its high specific capacity (3861 mAh/g) and low negative potential (- 3.04 V vs. NHE). However, the Li dendrite growth during Li deposition leads to serious safety problems and poor cycling performance. With durative forming and growing of the Li dendrite during cycling, the accompanying large surface area of SEI layers induces a constant loss of both working Li metal and electrolyte, leading to a low Coulombic efficiency and a rapid capacity decay. Thus, there has been much research effort to achieve the suppression of the Li dendrite formation. According to the previous reports, employing three-dimensional (3D) current collectors is one approach to reduce the effective current density and delay dendrite growth. In this study, we developed a strategy by impregnating Li metal into the 3D current collectors of nickel (Ni) foam and carbon (C) foam backbone to improve the cycling performance of Li-metal anodes for Li-metal batteries. As a result, Li @ Ni foam and Li @ C foam cells showed better capacity retention for 500 cycles than pure Li metal anodes.

Recently, great advance of the Li-S battery technology enables its penetration to the power source of the mid- and large-sized devices, which require high energy and power density that cannot be achieved in the Li-ion battery. While the most successful sulfur cathode could be designed by the optimization of the composite structure with carbonaceous materials, the binder system has been recently considered another important factor because the electrode structure of the sulfur cathode suffers huge structural change during the repeated electrochemical cycles. We studied the structural and electrochemical performance of the sulfur cathodes prepared by two different binders, the water-soluble SBR/CMC mixture binder and the traditional PVdF binder. The enhanced battery performance was observed in the SBR/CMC-based electrode and its origin was investigated by post mortem analysis about the electrodes, which confirmed the better mechanical integrity in the electrode compared with the PVdF-based electrode.

We introduce a new synthesis method to prepare small TiO 2 nanoparticles with a narrow particle size distribution, whichis achieved by electron beam (E-beam) irradiation. The effects of E-beam irradiation on the synthesis of TiO 2 nanoparticlesand the electrochemical performance of TiO 2 nanoparticles as alternative anode materials for Li-ion batteries are investi-gated. The TiO 2 nanoparticles induced by E-beam irradiation present better cycling performance and rate capability thanthe TiO 2 nanoparticles synthesized by normal hydrolysis reaction. The better electrochemical performance is attributed tosmall particle size and narrow particle size distribution, resulting in the large surface area that provides innumerable reacti onsites and short diffusion length for Li + through TiO 2 nanoparticles.Keywords : TiO 2 , nanoparticle, electron beam irradiation, anode material, Li-ion battery Received October 23, 2014 : Accepted January 27, 2015 1. Introduction Titanium oxide (TiO 2

Black TiO2−x nanotube arrays, which are synthesized by an electrochemical method and subsequent thermal conversion in a hydrogen atmosphere, are employed as binder-free, free-standing electrodes for high rate Li-ion microbatteries. Excellent cyclability and superior rate capability are achieved by an oxygen-deficient structure of TiO2 with increased electronic conductivity and the formation of metallic titanium hydride phases on the substrate.

Structurally stabilized Na3V2(PO4)3/C composite cathode materials with excellent electrochemical performance can be obtained by incorporating functional pillar ions into the structure. As pillar ions, K-ions have a larger ionic radius compared to Na-ions, and play an important role in enlarging the Na-ion diffusion pathway and in increasing the lattice volume by elongating the c-axis, thereby improving the rate performance. Furthermore, since the incorporated K-ions rarely participate in the electrochemical extraction/insertion reactions, they can stabilize the Na3V2(PO4)3 structure by suppressing significant lattice volume changes or structural distortion, even in a wide range of voltage windows accompanying multiple transitions of V ions and phase distortions. We investigated how the K-ion doping level affected the crystal structure and electrochemical properties of Na3V2(PO4)3 cathode materials for Na-ion batteries.

LiMn 1.5 Ni 0.5 O 4 and LiMn 1.5 Ni 0.5 O 3.9 Cl 0.1 are prepared by a solution-based process to investigate the influences of Cl doping on the structural and electrochemical properties of high voltage LiMn 1.5 Ni 0.5 O 4 cathode materials for Li-ion batteries. LiMn 1.5 Ni 0.5 O 3.9 Cl 0.1 features an improved cyclic performance at 30 °C and 55 °C compared with LiMn 1.5 Ni 0.5 O 4 , which originates from the enhanced structural stability by formation of strong Mn–Cl and Ni–Cl bonds revealed by XPS analysis. The improvement in the rate capability of LiMn 1.5 Ni 0.5 O 3.9 Cl 0.1 is attributed to the facilitated Li-ion diffusion in the lattice, due primarily to the larger ionic radius of Cl than that of O. From the GITT analysis, it is revealed that the Li-ion diffusivity of LiMn 1.5 Ni 0.5 O 3.9 Cl 0.1 is improved about 2 times compared with that of LiMn 1.5 Ni 0.5 O 4 . The improved Li-ion diffusivity in the lattice is assigned to the increase in the lattice constant of LiMn 1.5 Ni 0.5 O 3.9 Cl 0.1 compared with that of LiMn 1.5 Ni 0.5 O 4 by the doping of Cl.

We have designed a unique microstructure of graphene embedded LiFePO4 by a catalyst assisted self assembly method as a cathode material for high power lithium-ion batteries. The stable amide bonds between LiFePO4 and graphene were formed by the catalyst assisted self assembly. High conductive graphene provides a fast electron transfer path, and many pores inside the structure facilitate the lithium-ion diffusion. The graphene embedded LiFePO4 fabricated by the novel method shows enhanced cycling performance and rate-capability compared with that of carbon coated LiFePO4 as a cathode material for high power lithium-ion batteries.

The effect of styrene-butadiene rubber (SBR)/sodium salt of carboxymethyl cellulose (CMC) and poly(vinylidene fluoride) (PVdF) binders in the anodes on low-temperature performance and cyclability of automotive Li-ion batteries is investigated in 2.0 Ah cylindrical 18650 cells, composed of LiNi0.5Co0.2Mn0.3O2 as cathodes and graphite as anodes. The physical and electrochemical properties of SBR/CMC and PVdF anodes are characterized to compare their low-temperature performance. It is found that the adhesion strength of the SBR/CMC anode is slightly higher than that of the PVdF anode. On the other hand, because of its lower glass transition temperature (Tg), higher ionic conductivity and better absorption of the electrolyte, the PVdF anode results in higher electrical and ionic conductivity than observed in the SBR/CMC anode at low temperatures. These properties of the PVdF anode contribute to smaller impedance and faster Li-ion diffusion. Thus, the PVdF anode exhibits better discharge behavior and cycle performance at low temperatures than the SBR/CMC anode.

Recently, great advance of the Li-S battery technology enables its penetration to the power source of the mid- and large-sized devices, which require high energy and power density that cannot be achieved in the Li-ion battery. While the most successful sulfur cathode could be designed by the optimization of the composite structure with carbonaceous materials, the binder system has been recently considered another important factor because the electrode structure of the sulfur cathode suffers huge structural change during the repeated electrochemical cycles. We studied the structural and electrochemical performance of the sulfur cathodes prepared by two different binders, the water-soluble SBR/CMC mixture binder and the traditional PVdF binder. The enhanced battery performance was observed in the SBR/CMC-based electrode and its origin was investigated by post mortem analysis about the electrodes, which confirmed the better mechanical integrity in the electrode compared with the PVdF-based electrode.

LiMn2O4, Li1.05Mn1.95O4, and Li1.05Mn1.95O3.95Cl0.05 are prepared by a solution-based process to investigate the influences of codoping of Li and Cl on the electrochemical performance and structural stability of Li1+xMn2-xO4-yCly (x, y = 0, 0.05). Li1.05Mn1.95O3.95Cl0.05 features an improved cycling performance and rate capability compared with LiMn2O4 and Li1.05Mn1.95O4, which originate from the improved structural stability and the reduction in Mn dissolution into electrolyte by the codoping of Li and Cl. The improvement in the cycling performance of Li1.05Mn1.95O3.95Cl0.05 is more appreciable at a higher temperature. Further, the electrode resistance of Li1.05Mn1.95O3.95Cl0.05 is much lower than that of LiMn2O4 over the first charge, suggesting that LiMn2O4 with high electrode resistance is structurally unstable during cycling. Both the suppressed Mn dissolution and the reduced electrode resistance of Li1.05Mn1.95O3.95Cl0.05 are attributed to the reinforcement of MnO6 octahedral in Li1.05Mn1.95O3.95Cl0...

Porous and coarse (5–10 μm) LiFePO4/C composites with excellent electrochemical performance were synthesized by a growth technology using nanostructured (100–200 nm) LiFePO4 as seed crystals for th...

Ball-milling and subsequent microwave heating processes have been applied to synthesize VBO 3 –C composite. The samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, inductively coupled plasma mass spectroscopy, and electrochemical methods. The VBO 3 –C composite was successfully prepared after 30 min ball-milling and 13 min microwave heating. The synthesized VBO 3 –C composite was composed of well crystallized VBO 3 particles with well dispersed amorphous carbon and exhibited higher reversible capacity (625 mAh g −1 ) and improved cyclic performance than those in previous study.

The effects of vinylene carbonate (VC) on high temperature storage of high voltage Li-ion batteries are investigated. 1.3 M of LiPF6 dissolved in ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) of 3:3:4 volume ratio is used as original electrolyte for 18650 cylindrical cells with LiCoO2 cathode and graphite anode. VC is then added to electrolyte. At the initial stage of the high temperature storage, higher open-circuit voltage (OCV) is maintained when increasing the VC concentration. As the storage time increases, OCV of higher VC concentration drops gradually, and then the gas evolution takes place abruptly. Gas analysis shows methane (CH4) decreases with increase of the VC concentration due to formation of stable solid electrolyte interface (SEI) layer on the graphite. Since the residual VC after formation of the SEI layer decomposes on the cathode surface, carbon dioxide (CO2) dramatically increases on the cathode with the VC concentration, leaving poly(VC) film at the anode surface, as suggested by XPS test results.

The effects of chemical etching on lithium (Li) storage properties of single-walled carbon nanotubes (SWCNTs) were investigated. The SWCNTs were synthesized on supported catalysts by thermal chemical-vapor deposition method, purified, and chemically etched in an acid solution. The purified SWCNTs and the etched SWCNTs were electrochemically inserted and extracted with Li. The structural and chemical modifications in the etched SWCNTs change the Li storage properties of the etched SWCNTs. The reversible capacity (Crev) increases with the etching time, from 616 mAh g−1 (Li1.7C6) for the purified SWCNTs to 878 mAh g−1 (Li2.4C6) for the etched SWCNTs after etching for 10 h, and decreases slightly after further etching. The irreversible capacity (Cirr) also increases continuously with the etching time, from 1573 mAh g−1 (Li4.2C6) for the purified SWCNTs to 1772 mAh g−1 (Li4.8C6) for the etched SWCNTs after etching for 20 h. The insertion of Li ions into the etched SWCNTs is facilitated by various Li insertion sites formed during the chemical etching process. The Li ions inserted into various insertion sites enhance the Crev in the etched SWCNTs with the large voltage hysteresis by hindrance of the extraction of Li ions from the etched SWCNTs. During the charge/discharge cycling, the Li ions inserted into the etched SWCNTs are extracted easily at the initial stage of cycling, but an amount of the extracted Li ions from the etched SWCNTs decreases due to the accumulation of Li ions in the etched SWCNTs.

Lithium metal is the most attractive anode material for batteries because of its high specific capacity and low negative potential. However, lithium dendrite growth during lithium deposition leads to serious safety problems and poor cycling performance. According to the previous reports, the electrochemical performance of lithium metal anode material for LIBs highly depends on the composition and physicochemical properties of the electrolytes used. However, a key factor with regard to electrolytes that can determine the electrochemical characteristics of the anode materials is not fully understood yet. Thus, in the present work, we observed the electrochemical performance of lithium metal anode material as a function of electrolyte parameters, and elucidated the chemical/electrochemical reaction behavior of various electrolytes on the surface of lithium metal.

Na-ion batteries are currently the focus of significant research activity due to the relative abundance of sodium and its consequent cost advantages. Thus, enormous efforts have been made to improve the electrochemical performance of SIBs through the development of novel cathode materials. According to the previous literatures, P2-type layered cathode materials for SIBs have suffered from their low initial coulombic efficiency, which inevitably requires the pre-sodiation of carbon anode materials under full cell systems. In this regard, we focused on how to increase their initial charge capacity with sacrificial salts in the level of electrode fabrication. Thus, in the present study, we suggest new electrode fabrication process with sacrificial salts to reduce the high initial irreversible.

Sodium-ion rechargeable batteries (SIBs) have attracted great attention as promising next-generation rechargeable batteries, especially for large-scale energy storage systems (ESS), owing to the natural abundance of Na resources and the similarities in their chemical structure and reaction mechanism to commercial lithium-ion batteries (LIBs). Thus, enormous efforts have been made to improve the electrochemical performance of SIBs through the development of novel cathode materials. According to the previous literatures, P2-type layered cathode materials for SIBs have suffered from their low initial coulombic efficiency, which inevitably requires the pre-sodiation of carbon anode materials under full cell systems. In this regard, we focused on how to increase their initial charge capacity with sacrificial salts in the level of electrode fabrication. Actually, the suppression of irreversible capacity of P2-type layered cathode materials are challenging without specific electrode design. Thus, in the present study, we suggest new electrode fabrication process with sacrificial salts (i.e. NaN3) to reduce the high initial irreversible capacity of P2-type layered cathode materials for SIBs.

An electroplated copper/tin (Cu/Sn) anode with a layered structure is described that minimizes the high-voltage irreversible capacity observed in an electroplated Sn anode at a potential over 1 V. The high-voltage irreversible capacity is caused by the electrolyte decomposition at the catalytic site of the Sn anode. In the electroplated Cu/Sn anode, the upper Cu layer effectively suppresses the exposure of the newly formed Sn surfaces, resulting in the absence of the high-voltage irreversible capacity. Therefore, the electroplated Cu/Sn anode exhibits a higher cycle performance than the electroplated Sn anode.

The electrochemical properties of amorphous vanadium pentoxide (V2O5) thin films deposited by reactive r.f.-sputtering were investigated using galvanostatic charge/discharge cycling and galvanostatic intermittent titration technique (GITT). As x in Li x V2O5−y increased (x = 0–2.0), the electromotive force of the lithium (Li)∣1 M LiClO4–propylene carbonate∣Li x V2O5−y cell decreased gradually without a potential plateau or an abrupt potential reduction, demonstrating that an irreversible structural change did not occur in the entire Li content. Chemical diffusivity of the Li ion in the Li x V2O5−y thin film measured using GITT was determined to be 4 × 10−13–7 × 10−14 cm2 s−1 in the Li content range investigated.

The effects of ball-milling on Li insertion into multi-walled carbon nanotubes (MWNTs) are presented. The MWNTs are synthesized on supported catalysts by thermal chemical vapour deposition, purified, and mechanically ball-milled by the high energy ball-milling. The purified MWNTs and the ball-milled MWNTs were electrochemically inserted with Li. Structural and chemical modifications in the ball-milled MWNTs change the insertion–extraction properties of Li ions into/from the ball-milled MWNTs. The reversible capacity ( C rev ) increases with increasing ball-milling time, namely, from 351 mAh g −1 (Li 0.9 C 6 ) for the purified MWNTs to 641 mAh g −1 (Li 1.7 C 6 ) for the ball-milled MWNTs. The undesirable irreversible capacity ( C irr ) decreases continuously with increase in the ball-milling time, namely, from 1012 mAh g −1 (Li 2.7 C 6 ) for the purified MWNTs to 518 mAh g −1 (Li 1.4 C 6 ) for the ball-milled MWNTs. The decrease in C irr of the ball-milled samples results in an increase in the coulombic efficiency from 25% for the purified samples to 50% for the ball-milled samples. In addition, the ball-milled samples maintain a more stable capacity than the purified samples during charge–discharge cycling.

The structure and composition of Cr-nitrides formed on an electroplated hard Cr layer during an ion-nitriding process were analyzed, and its growth kinetics was examined as a function of the ion-nitriding temperature and time to establish a computer simulation model for the prediction of growth behavior of the Cr-nitride layer. The Cr-nitrides formed during the ion-nitriding at 550–770 °C were composed of outer CrN and inner Cr2N layers. A nitrogen diffusion model in the multilayer, based on fixed-grid finite difference method, was applied to simulate the growth kinetics of Cr-nitride layers. By measuring the thickness of Cr-nitride layers as a function of ion-nitriding temperature and time, the activation energy (Q) and nitrogen diffusion constant (Do) were determined for growth of CrN and Cr2N; the result was applied to simulate the growth kinetics of Cr-nitride layers, and reasonable good agreement was obtained with the experimental results.

To improve the cycle performance of the thick Sn electrode of 10 μm thickness, the Sn–C composite electrodes were fabricated by co-electrodeposition with two kinds of carbon particles which were the graphite and the acetylene black. The acetylene black particles were well dispersed in the Sn matrix more than the graphite particles. The carbon content in the Sn–C composite electrodes was measured about 12% of the graphite and 16% of the acetylene black particles. Even though carbon content of the Sn–acetylene black electrode was not significantly higher than that of the Sn–graphite electrode, the cycle performance of the Sn–acetylene black electrode was much higher than that of the Sn–graphite electrode. This demonstrates that the ‘buffering effects’ of well dispersed acetylene black particles was larger than that of the graphite particles. The cycle performance of the Sn–acetylene black electrode was significantly improved by the aging treatment. Keywords: Sn, Carbon, Electrodeposition, Cycle performance, Li-ion batteries

Porous and coarse (5-10 μm) LiFePO₄/C composites with excellent electrochemical performance were synthesized by a growth technology using nanostructured (100-200 nm) LiFePO₄ as seed crystals for the 2nd crystallization process. The porous and coarse LiFePO₄/C presented a high initial discharge capacity (∼155 mA h g⁻¹ at 0.1 C), superior rate-capability (∼100 mA h g⁻¹ at 5 C, ∼65 % of the discharge capacity at 0.1 C), and excellent cycling performance (∼131 mA h g⁻¹, ∼98 % of its initial discharge capacity after 100 cycles at 1 C). The improvement in the rate-capability of the LiFePO₄/C was attributed to the high reaction area resulted from the pore tunnels formed inside LiFePO₄ particles and short Li-ion diffusion length. The improved cycling performance of the LiFePO₄/C resulted from the enhanced structural stability against Li-deficient LiFePO₄ phase formation after cycling by the expansion of the 1D Li-ion diffusion channel in the LiFePO₄ crystal structure.

We report a new discovery for enhancing Li ion transport at the surface of Li3V2(PO4)3 particles through superionic pathways built along an ionic conductor. The Li3V1.95Zr0.05(PO4)3/C composite has much higher initial discharge capacity, superior rate-capability, and excellent cycling performance when compared with pristine Li3V2(PO4)3/C. This is partly due to the occupation of vanadium sites by Zr4+ ions in the Li3V2(PO4)3 host crystals and facile Li ion migration through a LiZr2(PO4)3-like secondary phase that forms on the surface of the Li3V1.95Zr0.05(PO4)3 particles. Our findings about high Li ion transport and structure stabilization induced by Zr incorporation suggests a breakthrough strategy for achieving high-power Li rechargeable batteries using NASICON-structured cathode materials in combination with nanoarchitecture tailoring. Figure 1

Single-walled carbon nanotube (SWCNT)/silicon composites were produced from the purified SWCNTs and Si powder by high-energy ball-milling and then electrochemically inserted with Li using Li/(SWCNT/Si) cells. The highest reversible capacity and lowest irreversible capacity of the SWCNT/Si composites were measured to be 1845 and 474 mAh g(-1) after ball-milling for 60 min, respectively. During the charge/discharge process, most of the Li ions were inserted into the SWCNT/Si composites by alloying with Si particles below 0.2 V and extracted from the SWCNT/Si composites by dealloying with Si particles around 0.5 V. The enhanced capacity and cycle performance of the SWCNT/Si composites produced by high-energy ball-milling were due primarily to the fact that SWCNTs provided a flexible conductive matrix, which compensated for the dimensional changes of Si particles during Li insertion and avoided loosening of the interparticle contacts during the crumbling of Si particles. The ball-milling contributed to a decrease in the particle size of SWCNTs and Si particles and to an increase in the electrical contact between SWCNTs and Si particles in the SWCNT/Si composites.

Li4Ti5O12 (LTO) with a spinel structure has received much attention as the most promising alternative to the conventional graphite anode material of Li-ion batteries for hybrid electric vehicle, electric vehicle, and large-scale energy storage applications, due primarily to its advantageous material properties, such as enhanced safety, good capacity retention during cycling, and high power density. Also, LTO is a zero-strain insertion material, which has excellent Li+ insertion/extraction reversibility with no volume change. In spite of these advantages, LTO presents a relatively poor rate capability due to its low electrical conductivity and Li+ diffusion coefficient. Recently, the nanostructured LTO materials coated with carbon-based materials have been extensively studied in the hope of achieving further improvement in the rate capability due to both good electrical conductivity and short Li+ diffusion length. However, these nanomaterials present relatively low volumetric energy density and difficulty in the electrode coating process, and also high production cost. Therefore, it is very important to develop a novel method to achieve simultaneously the enhanced electrical conductivity and volumetric energy density of LTO material. In this work, we suggest a facile method to achieve the improved electrochemical performance of LTO anode material composed of the micro-sized primary particles for high-power Li-ion batteries. The electrochemical performances of the micro-sized LTO particles, including the rate capability and cycling stability were significantly improved by hydrogenation. The hydrogenated LTO (denoted as H-LTO) particles were obtained by thermal annealing of the P-LTO (denoted as P-LTO) particles at 800 °C for 2~7 h in hydrogen atmosphere. Thermal annealing was performed in a quartz tube furnace filled with ultrahigh purity hydrogen gas. The H-LTO particles exhibited vastly superior the rate capability and capacity retention property during cycling to the P-LTO particles at high current density, since the insertion and extraction of Li+ through the H-LTO particles were preferable to those through the P-LTO particles, which were probably attributed to the short diffusion length for Li+, innumerable reaction sites, and relatively high electrical conductivity.

Lithium ion batteries have been widely studied due to their superior energy and power densities to utilize large scale applications such as electric vehicles and energy storage systems. In spite of extensive researches to overcome the problem of the lithium ion battery price, the large scale battery market has been sluggishly extended primarily due to the lack of lithium resources. Alternatively, sodium ion batteries are illuminated for the energy sources of the large scale energy storage system because of sufficient sodium sources. As a class of the sodium ion battery cathode materials, phosphate-based Na-insertion hosts (NaVPO4F, NaMPO4, Na1.5VOPO4F0.5, Na2FePO4F, NaTi2(PO4)3, etc.) with strong polyanion networks have received great attention due to their excellent structural and thermal stabilities. NASICON-Na3V2(PO4)3 is the one of the promising cathode materials for the sodium ion batteries. Na3V2(PO4)3 shows 117.6 mAh·g-1 theoretical capacity at 3.4 V vs. Na/Na+ in V4+/V3+ redox couple. It has strong PO4 polyanion networks which improve the safety of the large scale applications. Unfortunately, Na3V2(PO4)3 shows severe capacity fading at high rate because of the low electrical conductivity and ion diffusivity. In the phosphate-based active materials for Li or Na ion batteries, the addition of conductive materials and the substitution of transition metal or alkali metal with alien ions have been conducted to overcome these problems. Especially the substitution of Li ion with Na ion or K ion for the Li ion batteries shows better electrochemical performances due to the lattice expansion and narrowing the band gap. In this work, NASICON-Na3-xKxV2(PO4)3/C (x=0, 0.05, 0.10, and 0.15) are synthesized by a solid state reaction. By the doped K ion which is larger than Na ion (rK+ (1.52 Å) > rNa+ (1.16 Å)), the structure becomes enlarged and it makes Na ion migrate easily. Moreover the doped K ion in the structure even after charging contributes to the structural stability by reducing volume changes during cycling.

Titanium oxide (TiO2) has received much attention as the most promising alternative to the conventional graphite anode of Li-ion batteries for high energy and power. The performance of TiO2 anode for Li-ion batteries depends strongly on the crystalline phase, the morphology, and the porosity of the structure. The nanostructured TiO2 materials, such as nanoparticles, nanorods, nanowires, and nanotubes have been studied to improve the performance of TiO2 anode. Recently, it was reported that the hydrogenated TiO2, called a ‘black TiO2’ nanostructures are more attractive for photovoltaics, photocatalysis, and supercapacitors owing to their narrower bandgap (less than typical 3 eV value) and relatively high electrical conductivity. The smooth and well-ordered TiO2 nanotubes were synthesized on a Ti disk successfully by anodization in a non-aqueous solution containing fluoride ions. The as-prepared TiO2 nanotubes were annealed to obtain crystalline anatase (A-TiO2 NTs) and hydrogenated TiO2 nanotubes (H-TiO2 NTs) at 450 °C for 2 h in air and hydrogen atmosphere, and then their electrochemical performances were investigated as alternative anode materials for Li-ion batteries. The initial discharge capacity of the H-TiO2 NTs (0.117 mAh cm-2) was superior to that of the A-TiO2 NTs (0.110 mAh cm-2) and the discharge capacities of the H-TiO2 NTs and A-TiO2 NTs maintained nearly 72 and 44 % at a current density of 10 mA cm-2. In addition, the H-TiO2 NTs (89 %) exhibited much higher the capacity retention than the A-TiO2 NTs (70 %) at the current density of 1 mA cm-2 (~10 C-rate) after 300 cycles, as shown in Figure 1. The H-TiO2 NTs presented smaller the crystallite size and charge transfer resistance (Rc) compared with the A-TiO2 NTs and the oxygen vacancies were formed in the H-TiO2 NTs during hydrogenation, which was proved by the presence of Ti3+ from the XPS analysis. These results indicate that the insertion and extraction of Li+ through the H-TiO2 NTs were preferable to those through the A-TiO2 NTs, which were probably attributed to the short diffusion length for Li+, innumerable reaction sites, and relatively high electrical conductivity. Therefore, the H-TiO2 NTs exhibited vastly superior the rate capability and capacity retention property during cycling to the A-TiO2 NTs at high current density as anode materials for Li-ion batteries.

Lithium ion batteries have been widely studied due to their superior energy and power densities to utilize large scale applications such as electric vehicles and energy storage systems. In spite of extensive researches to overcome the problem of the lithium ion battery price, the large scale battery market has been sluggishly extended primarily due to the lack of lithium resources. Alternatively, sodium ion batteries are illuminated for the large scale energy storage system because of sufficient sodium sources. As a class of the sodium ion battery cathode materials, phosphate-based Na-insertion hosts (NaVPO4F, NaMPO4, Na1.5VOPO4F0.5, Na2FePO4F, NaTi2(PO4)3, etc.) with strong polyanion networks have received great attention due to their excellent structural and thermal stabilities. NASICON-Na3V2(PO4)3 is the one of the promising cathode materials for the sodium ion batteries. Na3V2(PO4)3 shows 117.6 mAh·g-1 theoretical capacity at 3.4 V vs. Na/Na+ in V4+/V3+ redox couple. It has strong PO4 polyanion networks which improve the safety of the large scale applications. Unfortunately, Na3V2(PO4)3 shows severe capacity fading at high rate because of the low electrical conductivity and ion diffusivity. In the phosphate-based active materials for Li or Na ion batteries, the addition of conductive materials and the substitution of transition metal or alkali metal with alien ions have been conducted to overcome these problems. Especially the substitution of Li ion with Na ion or K ion for the Li ion batteries shows better electrochemical performances due to the lattice expansion and narrowing the band gap. In this work, NASICON-Na3-xKxV2(PO4)3/C (x=0, 0.05, 0.10, and 0.15) are synthesized by a sol-gel method. By the doped K ion which is larger than Na ion (rK+ (1.52 ") > rNa+ (1.16 ")), the structure becomes enlarged and it makes Na ion migrate easily. Moreover the doped K ion in the structure even after charging contributes to the structural stability by reducing volume changes during cycling. As shown in Figure 1 (a), while undoped Na3V2(PO4)3/C and Na2.85K0.05V2(PO4)3/C exhibited the cell failures in 200 cycles at 1 C, Na2.90K0.10V2(PO4)3/C and Na2.85K0.15V2(PO4)3/C showed stable cycle performances without failure. Moreover, rate capabilities of Na2.90K0.10V2(PO4)3/C and Na2.85K0.15V2(PO4)3/C were significantly improved compared with those of undoped Na3V2(PO4)3/C and Na2.85K0.05V2(PO4)3/C, shown in Figure 1 (b). Especially Na2.90K0.10V2(PO4)3/C showed the best electrochemical performances among the four samples. The enhanced electrochemical performances were originated from the low polarization resistance due to the low charge transfer resistance and the high Na ion diffusivity. This excellent kinetic behavior mainly results from the pillar effect of K ion which provides the structural stability and enough space for Na ion diffusion. This advantageous pillar effect was verified by measuring the remained K content after cycling and the volume changes between the discharged phase and the charged phase. Therefore, Na3V2(PO4)3 with the proper amount of K doping in Na site might be regarded as promising cathode materials for Na ion rechargeable batteries.

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Nanostructured electrodes have recently received great attention as components in lithium rechargeable batteries, especially because of the high power produced by the fast kinetic properties of these unique structures. Here, we report the successful synthesis of various nanostructured morphologies of spinel lithium manganese oxide electrodes (nanorod, nanothorn sphere, and sphere) from a similarly shaped manganese dioxide precursor that was controlled with different aluminium contents by the hydrothermal method. Among these structures, nanothorn sphere structured LiAl0.02Mn1.98O4 produces the highest discharge capacity of 129.8 mA h g−1, excellent rate capability (94.6 mA h g−1 at 20 C, 72% of 0.2 C-rate discharge capacity) and stable cyclic retention for 50 cycles. The excellent kinetic properties of the nanothorn sphere structure are not only due to the nanothorn sphere electrode having high surface area but also because the critical amount of Al in the nanothorn sphere electrode was located at the Mn site (16d) instead of the Li site (8a).

Multi-walled carbon nanotube (MWNT)/silicon composites with different weight ratios were produced from purified MWNTs and Si powder by high energy ball-milling and then electrochemically inserted with lithium. The charge/discharge properties for the ball-milled MWNT/Si composite anodes were found to be very sensitive to the weight ratio of MWNT to Si. The highest Crev and lowest Cirr of the composite anode were measured to be 1770 mAh/g and 469 mAh g-1 respectively at the ratio of MWNT0.5/Si0.5. During charging/discharging processes, most of Li ions were inserted into the ball-milled MWNT/Si composites by alloying with Si particles at potentials positive to 0.25 V vs. Li, and extracted from the ball-milled MWNT/Si composites by dealloying with Si particles at potentials positive to 0.5 V vs. Li. The good capacity and cycle performance of the MWNT0.5/Si0.5 composite anode is due primarily to the fact that MWNTs encapsulating fine Si particles by strong contact prevent Si particles from electrical insulation caused by the crumbling of the Si particles.