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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.

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.

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.

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.

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...

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.

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.

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.

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.