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Layered Ni-rich Li[Ni 0.6 Mn 0.2 Co 0.2- x Sn x ]O 2 cathode active materials with x  = 0–0.05 are synthesized via a co-precipitation synthesis route and the effect of doping content on the structural behavior and electrochemical performance are investigated. All synthesized materials show a well-defined layered structure of the hexagonal α -NaFeO 2 phase (space group R 3 ¯ m ) analyzed by X-ray diffraction (XRD). Electrochemical Li-metal/cathode cell studies exhibit that a Sn-content of 1%–2% is beneficial regarding specific discharge capacity and cycle life (≥20%). Detailed electrochemical investigations of Li-metal and lithium ion cells with cathodes consisting of LiNi 0.6 Mn 0.2 Co 0.2 O 2 and LiNi 0.6 Mn 0.2 Co 0.18 Sn 0.02 O 2 are conducted. Post mortem analyses by means of ICP-OES and TXRF show beneficial effects of the Sn-doping with regard to a lower transition metal dissolution and a higher available Li content in the cathode active material. The thermal analyses (TGA, DSC, ARC) show a stabilizing effect of Sn-doping, which results from a lower mass loss and less heat evolution of the charged cathode active materials at elevated temperatures. [ABSTRACT FROM AUTHOR]

In this work, we select four types of substitute cations, Ti 4+ , Al 3+ , Mg 2+ and Zn 2+ , to compare their influence on LiNi 0.8 Co 0.1 Mn 0.1 O 2 . After modification, the average lengths of Ni O bonds are elongated with the turn of the Ti , Al , Mg , pristine and Zn-substituted, namely the bond energies are diminished with this sequence, according to their roughly inverse square relation. This tendency is also obeyed by oxygen defects, which induces the Ni Li exchanging and surface decomposition, and then exert the effect on electrochemical behavior of Ni-rich cathodes. Among the investigated samples, the Ti-modified sample, which possesses the highest Ni O bond energy, presents the best cyclic stability and rate capability, retaining 93.8% in the 200 th cycle and 155.1 mAh g −1 under 5C, which is ∼12% higher than the pristine sample. Our approaches illustrate the importance of Ni O network and provide a novel thought to further improve these promising cathodes. [ABSTRACT FROM AUTHOR]

The electrochemical performances of LiMnNiCoO cathode material are enhanced through hydrothermal approach using NaS solution as a medium. Furthermore, the influence of contents of NaS solution on the morphology, structure, and electrochemical performances is fully investigated. The results indicate that a high content of NaS solution results in the formation of spinel particles which are detected by SEM, XRD, and HR-TEM measurements. The formation of spinel particles leads to a deterioration of electrochemical performances. However, a low content of NaS solution results in a slight structure change from layered phase to spinel one near the edge of LiMnNiCoO particles. This slight structure change facilitates the decrease of charge transfer resistance, which contributes to the enhanced rate capability of NaS-treated LiMnNiCoO. [ABSTRACT FROM AUTHOR]

Cathode materials LiMn 0.5 Fe 0.5 PO 4 /C and LiMnPO 4 /C were synthesized by a high-energy ball-milling assisted sol-gel method. The LiMn 0.5 Fe 0.5 PO 4 consists of nanorods and nanoparticles homogeneously wrapped with highly ordering carbon. The increased Néel-temperature and decreased effective magnetic moment of LiMn 0.5 Fe 0.5 PO 4 /C revealed the microstructure differences from LiMnPO 4 /C. Meanwhile, tiny amount of ferromagnetic impurities is detected in LiMn 0.5 Fe 0.5 PO 4 /C by magnetic tests. The synergetic effects of Fe substitution and carbon coating remarkably improve rate capacity and cyclic stability of LiMn 0.5 Fe 0.5 PO 4 /C. This solid solution delivers initial discharge capacities of 128.6 mAh g −1 and 116.3 mAh g −1 and capacity retentions of 93.5% and 90.3% after 100 cycles at 1C and 2C respectively, significantly better than LiMnPO 4 /C. [ABSTRACT FROM AUTHOR]

Li- and Na-transition metal fluorosulfate materials (AFeSO 4 F, A = Li, Na) are proposed as highly promising novel cathode materials for Li- and Na-ion batteries. In this study, the electrochemical performance and elastic properties of AFe 1- x M x SO 4 F (A = Li, Na; M = Co, Ni, Mg; x = 0, 0.5, 1) are investigated from the view of first-principles calculations. The computational results reveal that the substitutions of Fe by Ni, Co and Mg enhance the intercalation voltage of the fluorosulphate materials. The density of states analysis shows that transition metal-doping AFeSO 4 F, especially for Ni doping case, could achieve better electronic conductivity in comparison with the pure phase and Mg-doped AFeSO 4 F. Further bader charges calculations give a confirmation that the Fe and Co in AFe 0.5 Co 0.5 SO 4 F play significant role in the charge transfer during delithiated or desodiated progresses, but the relatively inert character of Ni and Mg is discovered in AFe 0.5 Ni 0.5 SO 4 F and AFe 0.5 Mg 0.5 SO 4 F. LiFeSO 4 F and NaFeSO 4 F are found to be ductile from the exploration of elastic constants, whereas their delithiated and desodiated configurations have brittle character. In addition, Young’s Modulus ( E ), and Poisson's Ratio ( ν ) for LiFeSO 4 F, NaFeSO 4 F and 50% metal-doped AFe 1- x M x SO 4 F (A = Li, Na; M = Co, Ni, Mg) are also presented to explore the hardness, bond characteristic and stability against shear. [ABSTRACT FROM AUTHOR]

Controlling architecture of electrode composites is of particular importance to optimize both electronic and ionic conduction within the entire electrode and improve the dispersion of active particles, thus achieving the best energy delivery from a battery. Electrodes based on conventional binder systems that consist of carbon additives and nonconductive binder polymers suffer from aggregation of particles and poor physical connections, leading to decreased effective electronic and ionic conductivities. Here we developed a three-dimensional (3D) nanostructured hybrid inorganic-gel framework electrode by in situ polymerization of conductive polymer gel onto commercial lithium iron phosphate particles. This framework electrode exhibits greatly improved rate and cyclic performance because the highly conductive and hierarchically porous network of the hybrid gel framework promotes both electronic and ionic transport. In addition, both inorganic and organic components are uniformly distributed within the electrode because the polymer coating prevents active particles from aggregation, enabling full access to each particle. The robust framework further provides mechanical strength to support active electrode materials and improves the long-term electrochemical stability. The multifunctional conductive gel framework can be generalized for other high-capacity inorganic electrode materials to enable high-performance lithium ion batteries. [ABSTRACT FROM AUTHOR]

In this work we compare electrochemical cycling stability of Fe containing Li rich phase Li 1.2 Ni 0.13 Fe 0.13 Mn 0.54 O 2 (Fe–Li rich) with the well-known Co containing Li rich composition Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 (Co–Li rich). During the first charge, the activation plateau corresponding to removal of Li 2 O from the structure is smaller (removal of 0.6 Li) in the case of Fe–Li rich compared to Co–Li rich composition (0.8 Li removal). Consequently, the Fe compound shows better capacity retention; for example, after 100 cycles Fe–Li rich compound exhibits 20% capacity degradation where as it is about 40% in the case of Co–Li rich phase. The electrochemical and microscopy studies support the fact that compared to Co–Li rich compound, the Fe–Li rich composition display smaller voltage decay and reduced spinel conversion. XPS studies on charged/discharged Fe–Li rich samples show participation of Fe +3 /Fe +4 redox during electrochemical cycling which is further supported by our first principles calculations. Also the temperature dependent magnetic studies on charge-discharged samples of Fe–Li rich compound point out that magnetic behavior is sensitive to cation oxidation states and Ni/Li disorder. [ABSTRACT FROM AUTHOR]

Introducing the Mg ion into host lattice is applied to improving the electrochemical performance of LiNi 0.6 Co 0.2 Mn 0.2 O 2 . The effect of Mg substitution for Co on the structure, morphology, electrochemical properties and Li + diffusion coefficients are investigated in details. Rietveld refinement results reveal that Mg is incorporated into the bulk lattice, which results in reduced cation mixing and expand c -lattice parameter. All Mg-doped sample exhibit better cycle and rate performances, although the Mg substitution for Co led to decreasing a part of capacity. The Li diffusion coefficients obtained by galvanostatic intermittent titration technique (GITT) are increased with increases of Mg content. [ABSTRACT FROM AUTHOR]

High-purity micro-rod β-Na 0.33 V 2 O 5 particles 2–5 μm in width and 3–10 μm in length are prepared by the chemical switch method. Electrochemical characterization demonstrates that micro-rod β-Na 0.33 V 2 O 5 as a cathode material for lithium ion batteries provides high discharge capacity, good rate-capability, and cyclic stability. It delivers high discharge capacities of 297, 245, 220, and 178 mAh g −1 at current densities of 0.1, 0.2, 0.5, and 1 C-rate, respectively. The capacity fading rate is less than 1% per cycle, with high volumetric discharge capacities (504 mAh cm −3 at 0.1C and 301 mAh cm −3 at 1 C). Scanning electron microscopy images of the micro-rods during cycling indicate that they have excellent crystal structural reversibility in the voltage range of 1.5–4.0 V. These superior electrochemical properties are attributed to the tunneled crystal structure and internal pores formed by crystal defects in the micro-rods. [ABSTRACT FROM AUTHOR]

Natural graphite treated by mechanical activation can be directly applied to the preparation of LiV(PO). The carbon-coated LiV(PO) with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that LiV(PO) (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g at 0.1 C and 162.9 mAh g at 1 C in the voltage range of 3.0-4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries. [ABSTRACT FROM AUTHOR]

We simulate the electrochemical properties of Li-ion cells consisting of a blended cathode composed of LiMn 2 O 4 and LiNi 0.6 Co 0.2 Mn 0.2 O 2 and an artificial graphite anode using the Li-ion battery model available in COMSOL MULTIPHYSICS 4.4 along with a capacity fade model. The discharge profiles of the pure and blended cathodes at various current rates obtained through simulations and experimental results are well matched. By combining two capacity fade models available in literature, namely the solid electrolyte interphase (SEI) growth model and the Mn 2+ dissolution model, the cycling performance of the pure LiMn 2 O 4 cells at 25 °C are successfully simulated and found to be in a good agreement with the experimental results. The blended cathode exhibits better capacity retention than the pure LiMn 2 O 4 during cycling. We also observed that at high powers, the gravimetric energy density of the LiMn 2 O 4 cathode exceeds that of the LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode; the reverse effect is seen at low powers. Further, we were able to easily modulate the energy and power densities of the blended cathode system by changing the blend ratio in our simulation model. [ABSTRACT FROM AUTHOR]

Li 3 V 2 (PO 4 ) 3 /C (LVP/C) cathode materials for lithium ion batteries have been successfully synthesized via carbon thermal reduction method using pitch as both a new carbon source and a reduction agent. The influences of different carbon sources (pitch, Super P, KS15 and Vulcan-XC72) and heat treatments between 650 and 950 °C on the LVP/C materials have also been investigated. The structural and electrochemical properties of the samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM) and high resolution transmission electron microscopy (HRTEM) as well as charge-discharge experiments. The LVP/C synthesized with pitch have smooth surface with uniform residue carbon distribution and presents the best electrochemical performance. In addition, the oxidation of carbon has been discussed. The results indicate that carbons obtained from four carbon sources are tended to be oxidized to CO 2 than CO. Electrochemical tests show the LVP/C-750 °C exhibits the highest discharge capacity and the most excellent capacity retention. Spherical LVP/C particles are obtained using the spray drying method. The spray drying-LVP/C composite deliver higher discharge capacity than those of LVP/C composites obtained by carbon thermal reduction method or by drying with oven. [ABSTRACT FROM AUTHOR]

MoO 3 -coated Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 cathode materials were synthesized via using co-precipitation method and wet coating process, and their crystal structure and particle morphology were analyzed and observed by XRD, SEM and TEM. The electrochemical properties of these materials were investigated and analyzed by using charge-discharge tests and electrochemical impedance spectroscopy. The results showed that the surface coating on Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 cathode was composed of α-MoO 3 and Li 2 MoO 4 , and the electrochemical properties were improved after coated with MoO 3 thin films. The initial coulombic efficiencies increased from 71.2% to 79.3% when the MoO 3 content increased to 5 wt.%. Particularly, the 3 wt.% MoO 3 -coated Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 showed the highest capacity retention of 90.8% after 100 cycles, and possessed the excellent rate discharge performance. The electrochemical impedance spectroscopy (EIS) and cyclic voltammetric results demonstrated that the layered MoO 3 coating could restrain the increment of the charge transfer resistance and stabilize the active material structure during cyclic process. [ABSTRACT FROM AUTHOR]

LiNi 0.5 Co 0.2 Mn 0.3 O 2 is successfully coated with Li 2 ZrO 3 through a simple sol–gel method. The formation of a uniform Li 2 ZrO 3 coating layer on the surface of the bare sample is confirmed by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectrometer (EDS). Similar discharge capacities are delivered by both bare and Li 2 ZrO 3 -coated samples. However, the capacity retention of Li 2 ZrO 3 -coated sample is much higher than that of the bare one at 1 C after 100 charge–discharge cycles under a high cutoff voltage of 4.6 V. Meanwhile, the rate performances of Li 2 ZrO 3 -coated sample are dramatically enhanced especially at high rates. Furthermore, the increase of impedance during charge–discharge process is suppressed by Li 2 ZrO 3 coating layer. [ABSTRACT FROM AUTHOR]

LiNi 0.5 Co 0.2 Mn 0.3 O 2 is successfully coated with Li 2 ZrO 3 through a simple sol–gel method. The formation of a uniform Li 2 ZrO 3 coating layer on the surface of the bare sample is confirmed by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectrometer (EDS). Similar discharge capacities are delivered by both bare and Li 2 ZrO 3 -coated samples. However, the capacity retention of Li 2 ZrO 3 -coated sample is much higher than that of the bare one at 1 C after 100 charge–discharge cycles under a high cutoff voltage of 4.6 V. Meanwhile, the rate performances of Li 2 ZrO 3 -coated sample are dramatically enhanced especially at high rates. Furthermore, the increase of impedance during charge–discharge process is suppressed by Li 2 ZrO 3 coating layer. [ABSTRACT FROM AUTHOR]

A novel 2Li 3 V 2 (PO 4 ) 3 ·LiV 3 O 8 composite with short rod and thin plate shapes is synthesized through sol–gel method followed by hydrothermal and solid–state reaction. LiV 3 O 8 is used as an additive to improve the capacity of Li 3 V 2 (PO 4 ) 3 . In the composite cathode, active impurity phase Li 0.3 V 2 O 5 is also present, which has little impact on the whole electrochemical properties. The 2Li 3 V 2 (PO 4 ) 3 ·LiV 3 O 8 composite delivers a high initial capacity of 162.8 mAh g −1 at a current density of 100 mA g −1 in the voltage range of 2.0–4.3 V. Furthermore, the composite with high crystallinity also shows high electrochemical reversibility and good rate capability. The diffusion coefficient of Li ions in the composite is in the range of 10 −11 –10 −9 cm 2 s −1 obtained from galvanostatic intermittent titration technique. [ABSTRACT FROM AUTHOR]

LiFePO 4 /graphene active material (LFP/G) was successfully synthesized via a simple, low raw material cost and environment friendly hydrothermal method at 170 °C. LFP/G composite was prepared in a template-free method using graphene nano-sheets as a conductive additive (3.0 wt.%) without any carbon coating. Results indicated the presence of LFP crystallites of the olivine phase, which are randomly anchored on the surface of graphene. Electrochemical characteristics of the LFP/G modified electrode show well-defined peaks, smaller peak potential separation and higher cycling stability compared to those of the pristine LFP obtained in the absence of graphene. LFP/G delivered an initial discharge capacity of 157 mA h g −1 at 0.2 C and 114 mA h g −1 at 5 C and the values were compared to those of LFP (the capacities reach up to 120 mA h g −1 at 0.1 C and 50 mA h g −1 at 5 C). The electrochemical enhancement of LFP/G could be mainly ascribed to synergetic effects of bridging graphene nanosheets and creating an interconnected conducting network of cross-linking between neighboring crystallites. Such network would enhance the stability of the cathode composite and buffer spaces to accommodate the volume pulsation during charge/discharge cycling. [ABSTRACT FROM AUTHOR]

Carbon-coated LiMnSiO powders were synthesized by a citric acid-assisted sol-gel process, and their physical and electrochemical properties were characterized to assess their suitability as a cathode material in lithium-rechargeable batteries. Carbon was coated onto the LiMnSiO particles through the carbonization of polymeric materials that were caused by the addition of citric acid during the sol-gel process. The particle size and electrical conductivity of the LiMnSiO powders were found to be changed by varying the amount of citric acid added during the sol-gel process. XRD analysis showed that the quantity of impurities in LiMnSiO was decreased during the sol-gel process. The carbon coating led to an increase in conductivity and mean particle size by creating an electrical and physical connection between the particles. The discharge capacity of LiMnSiO with over 5 % carbon coating was significantly increased to ~125 mAh g compared to just ~3 mAh g for noncoated material. [ABSTRACT FROM AUTHOR]

α-MoO nanobelts were synthesized by simple hydrothermal method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Cyclic voltammogram (CV) and galvanostatic charge/discharge testing techniques were employed to evaluate electrochemical behaviors of α-MoO materials. Results showed that α-MoO nanobelts with about 80 nm in diameter and 5-12 μm in length were grown in the orthorhombic system. Electrochemical characterisation confirmed that in lithium ion insertion/extraction process, the first intercalation of lithium ion in α-MoO at about 2.8 V was irreversible, corresponding to LiMoO (0 < x ≤ 0.25) and the parent MoO materials coexisting, the second lithium ion inter-calation was reversible at the potential range of 2.2-2.4 V followed by LiMoO (0.25 < x ≤ 0.5), and below 1.0 V the mechanism of lithium ion storage changed from lithium ion intercalation reaction into lithium alloying reaction. The α-MoO nanobelts showed better electrochemical performance, 319 mA h g initial discharge capacity, around 52% capacity retention after 20 cycles than that of α-MoO bulk. [ABSTRACT FROM AUTHOR]

A series of RuO 2 modified LiNi 0.5 Mn 1.5 O 4 materials are successfully prepared by the precipitation method. X-ray photoelectron spectroscopy confirms the presence of Ru 4+ in the materials. Scanning electron microscope and high resolution transmission electron microscope show that RuO 2 covers the surface of LiNi 0.5 Mn 1.5 O 4 particles. The amounts of RuO 2 in the materials are determined to be 1.6 wt.%, 2.0 wt.% and 3.0 wt.%, respectively. The electrochemical kinetics of the materials is studied by cyclic voltammetry and electrochemical impedance spectroscopy. The results show that RuO 2 modification decreases the polarization of the electrode, prevents the side reactions of the electrode and the electrolyte, and improves the charge transfer reactions at the electrode interface, all of which are beneficial for the electrochemical properties of LiNi 0.5 Mn 1.5 O 4 . In all samples tested, the one containing 2.0 wt.% of RuO 2 exhibits superior electrochemical performance. It shows discharge capacities of 131.7 mAh g −1 (room temperature) and 129.7 mAh g −1 (60 °C) at the 0.5 C rate with the corresponding capacity retention of 97.7% and 97.2% after 100 cycles. In addition, the material delivers high discharge capacities of 104.5 mAh g −1 at the 5 C rate and 66.1 mAh g −1 at the 10 C rate, demonstrating its excellent rate capability. [ABSTRACT FROM AUTHOR]

Compared with thermally exfoliated graphene oxide (TEGO) prepared at high temperature of 800 °C and a long time of 12 h, microwave exfoliated graphene oxide (MEGO) is successfully synthesized at 800 W for 2 min benefiting from “inert and instant heating” of microwave irradiation and employed to optimize electrochemical performance of LiFePO 4 . The as-obtained LiFePO 4 /MEGO exhibits overwhelming superiorities to LiFePO 4 /TEGO, particularly in high-rate performance. Although LiFePO 4 /MEGO delivers the similar specific capacity of 158.1 mAh · g −1 as well as the LiFePO 4 /TEGO at the rate of 0.1 C, the LiFePO 4 /MEGO performs smaller polarization of 53.3 mV resulting in better specific energy of 518.1 Wh · kg −1 and energy efficiency of 89.8%. Even at the high rate of 10 C and 20 C, the LiFePO 4 /MEGO delivers excellent specific energy of 300.3 Wh · kg −1 and 229.7 Wh · kg −1 (with corresponding specific capacity of 104.3 mAh · g −1 and 87.3 mAh · g −1 respectively), much better than those of the LiFePO 4 /TEGO. After 2000 cycles, the LiFePO 4 /MEGO still performs excellent rate capabilities with 91.2% and 83.8% retention respectively. [ABSTRACT FROM AUTHOR]

Abstract: A shell/core Co-incorporated LiMn2O4 cathode material was synthesized by a facile modified sol–gel process, using highly dispersed Mn3O4 nanoparticles as the Mn source. Structural characterization revealed that the shell layer, which was 5–10nm thick, and composed of spinel LiMn1.83Co0.17O4, grew homogeneously on the spinel LiMn2O4 core with a size of ~50nm. Electrochemical results showed that electrochemical performance of the shell/core cathode material compared favorably with that of the Co-doped LiMn2O4 counterparts. Also its rate capability and cycling performance were apparently superior to those of pristine LiMn2O4 synthesized under the same conditions. The shell/core cathode material exhibited a discharge capacity of 127mAhg−1 at a current rate of 0.5C (where 1C=148mAg−1), and retained a capacity of 103mAhg−1 at 10C, showing 81% capacity retention. After 200 cycles at 1C and 25°C, it delivered a capacity of 123mAhg−1, retaining 98% of its initial capacity. After 100 cycles at 1C and 55°C, it showed a capacity of 118mAhg−1, preserving 94% of its initial capacity. Its excellent electrochemical performance along with the facile synthesis process allowed the shell/core cathode material to serve as a promising cathode for high-performance Li-ion batteries. [Copyright &y& Elsevier]

Highlights: [•] Carbon-coated V2O5 was synthesized in a scalable and easy method using a carbon form as a template. [•] Electrochemical performance of the carbon-coated V2O5 was significantly improved compared to nano-sized V2O5. [•] The carbon-coated V2O5 calcined at 400°C showed enhanced capacity retention and rate capabilities. [ABSTRACT FROM AUTHOR]

A novel wet method of (NH4)3AlF6 coating was explored to enhance the electrochemical performance of Mn-based solid-solution cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2. The X-ray powder diffraction patterns show that the coating material is pure-phase (NH4)3AlF6 and both pristine and coated samples can be indexed to hexagonal α-NaFeO2 layered structure with space group of R-3m. The field-emission scanning electron microscope images and the energy dispersive X-ray spectroscopy show that (NH4)3AlF6 is successfully coated on the surface of active particle. The (NH4)3AlF6 coated electrodes exhibit improved electrochemical performance, for instance, the initial charge-discharge efficiency was promoted by 5% (NH4)3AlF6 coating, the 1wt.% and 3wt.% coated electrodes deliver elevated cycling ability which is ascribed to the lower resistance between electrode and electrolyte as indicated by AC impedance measurement at different cycles. In addition, the coated-electrodes also give enhanced rate capability particularly for 1wt.% NAF-coated electrode performing surprising capacity of 143.4 mAh g−1 at 5C higher than that of 109.4 mAh g−1 for pristine electrode. Furthermore, the 1wt.% NAF-coated electrode also shows improved cycle and rate performance at 55°C. [ABSTRACT FROM AUTHOR]

Abstract: LiVO3 materials are synthesized by combustion method with oxalic acid as fuel. Owing to its relatively low crystallization and small particle size, the LiVO3 calcined at 450 °C for 2 h displays optimal electrochemical performances, delivering a high discharge capacity of 298.4 mAh g−1 and 262.5 mAh g−1 between 1.0 and 3.5 V at a current density of 50 mA g−1 and 500 mA g−1 respectively, and exhibiting good cyclic stability. In this work, the chemical diffusion coefficient of Li+ (D Li+) in the LiVO3 electrode is determined by electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The value calculated by EIS is in the range of 10−9–10−8 cm2 s−1, while it calculated by GITT is 10−9.5–10−8 cm2 s−1. [Copyright &y& Elsevier]

Highlights: [•] An improved sol–gel method was developed to synthesize Li3V2(PO4)3/C cathode material. [•] The pH value had an obvious influence on the morphologies of the prepared powders. [•] Powders prepared at pH=4 had uniform size distribution with little agglomeration. [•] Powders prepared at pH=9 had a small particle size. [•] Discharge capacity and cycle performance were improved by changing pH value. [ABSTRACT FROM AUTHOR]

First-principles prediction of enhancement in the electrochemical potential of LiCoO with aluminum substitution has been realized through earlier experiments. For safer and less expensive Li-ion batteries, it is desirable to have a similar enhancement for alternative cathode materials, LiFePO and LiCoPO. Here, we present first-principles density functional theory based analysis of the effects of aluminum substitution on electrochemical potential of LiCoO, LiFePO and LiCoPO. While Al substitution for transition metal results in increase in electrochemical potential of LiCoO, it leads to reduction in LiFePO and LiCoPO. Through comparative topological analysis of charge density of these materials, we identify a ratio of Bader charges that correlates with electrochemical potential and determine the chemical origin of these contrasting effects: while electronic charge from lithium is transferred largely to oxygen in LiCoO, it gets shared by the oxygen and Co/Fe in olivine phosphates due to strong covalency between O and Co/Fe. Our work shows that covalency of transition metal-oxygen bond plays a key role in determining battery potential. [ABSTRACT FROM AUTHOR]

Abstract: Cube-like and plate-like Li[Li0.2Mn0.54Ni0.13Co0.13]O2 particles are obtained after treated in LiCl and KCl molten salts at 800 °C, respectively, comparing to the ball-like original particles calcined in air. The oxide treated in KCl molten salt with large specific area of 17.05 m2 g−1 delivers high discharge capacities of 254.1 mAh g−1 and 168.5 mAh g−1 at current densities of 200 mA g−1 and 2000 mA g−1, respectively. In addition, enhanced cycle stability with capacity retention of 94.9% after 80 cycles at charge–discharge current densities of 200 mA g−1 is obtained for the oxide treated in LiCl molten salt with sacrifice of a little capacity. Such electrochemical performance change is proved to be independent of Li+ diffusion coefficient. It appears that the treatment in molten salts can effectively reform the electrochemical performances of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode materials for various applications. [Copyright &y& Elsevier]

Abstract: Rechargeable lithium-ion batteries (LIBs) are currently accepted to be one of the most suitable energy storage resources in portable electronic devices because of their high gravimetric and volumetric energy density. To understand the behavior of Li+ ions on electrochemical lithium extraction/insertion process, we performed in situ 7Li nuclear magnetic resonance (NMR) measurements for LiCoO2 cathode in a plastic cell battery, and the spectral evolutions of the 7Li NMR signal of Li x CoO2 (0≤ x ≤1) were well investigated. Very narrow solid solution region of Li x CoO2 (∼0.99≤ x <1) was explicitly defined from the large intensity reduction of LiCoO2 signal at ∼0ppm, which is related to the localized nature of the electronic spin of paramagnetic Co4+ ion formed at the very early delithiation stage. With further decreasing the signal intensity of LiCoO2, a Knight-shifted signal corresponding to an electrically conductive Li x CoO2 phase emerged at x =0.97, which then monotonously decreased in intensity for x <0.75 in accordance with the electrochemical lithium de-intercalation from Li x CoO2. These observations acquired in situ fully confirm the earlier studies obtained in ex situ measurements, although the present study offers more quantitative information. Moreover, it was shown that the peak position of the NMR shift for Li x CoO2 moved as a function of lithium content, which behavior is analogous to the change in its c lattice parameter. Also, the growth and consumption of dendritic/mossy metallic lithium on the counter electrode was clearly observed during the charge/discharge cycles. [Copyright &y& Elsevier]

Highlights: [•] Li2+x Mn1−x P x Si1−x O4/C are novel cathode materials for lithium ion batteries. [•] Single phase Li2+x Mn1−x P x Si1−x O4/C is formed when x is not higher than 0.05. [•] Li2.05Mn0.95P0.05Si0.95O4/C (x =0.05) has the best electrochemical properties. [ABSTRACT FROM AUTHOR]

Abstract: LiNi1/3Co1/3Mn1/3O2 (LNCM) with a well-ordered layered structure, confirmed by X-ray diffraction, was synthesized by the chemical-wet synthesis incorporated with (i) a pulse microwave-assisted heating of LNCM precursors and (ii) a carbon coating technique. The microwave irradiation periods (i.e., 5–20min) and amount of carbon additive (i.e., glucose content: 0.1–0.75%) served as key factors in modifying as-prepared LNCM powders. The electrochemical performance of as-prepared LNCM cathodes was well characterized by cyclic voltammetry and charge–discharge cycling at 0.1–5C. Both appropriate microwave heating and carbon coating significantly improve discharge capacity, rate capability, and cycling stability of LNCM cathodes. This improved performance can be attributed to the facts that an appropriate microwave heating of LNCM precursors induces low cation mixing of the layered lattices and the carbon coating enables the creation of outer circuit of charge-transfer pathway, preventing cathode corrosion from direct contact to the electrolyte. The C-coated LNCM cathode shows the increased capacity retention from 70.2 to 93.3% after 50 cycles at 1C. On the basis of the experimental results, both the microwave heating and the carbon coating provide a feasible potential way to improve the electrochemical performance of LNCM cathode, benefiting the development of Li-ion batteries. [Copyright &y& Elsevier]

Abstract: Li2MnSiO4 cathode materials doped with various cationic ions, Ga3+, Al3+, and Mg2+, are synthesized and their microstructure and electrochemical properties are investigated. The samples doped with trivalent ions, especially Ga3+, lead to a higher charge/discharge capacity and initial efficiency with well-dispersed nanoparticle formation. We can realize that the enhanced electrochemical performance of the specific ion doped Li2MnSiO4 cathodes originated from the uniformly distributed nanoparticles rather than the additional lithium insertion/extraction of the given cathode materials induced by the charge compensation. [Copyright &y& Elsevier]

Abstract: Lithium-rich layered cathode Li1.2Mn0.54Ni0.13Co0.13O2 is synthesized by a co-precipitation method followed by high-temperature treatment and surface coated with different amount of amorphous FePO4. The microstructure and electrochemical performance of the as-prepared cathode materials are investigated systematically. It is demonstrated that the Li1.2Mn0.54Ni0.13Co0.13O2 particles are uniformly coated with amorphous FePO4. With proper amount of amorphous FePO4 coating layer, significant improvements in discharge capacity, initial Coulombic efficiency, rate capability, cycle performance, and thermal stability are achieved at room temperature. Specifically, the 3 wt.% FePO4-coated cathode exhibits the highest discharge specific capacities (271.7 mAh g−1 at C/20), improved initial Coulombic efficiency (85.1%), and best cyclability (discharge capacity of 202.6 mAh g−1 at C/2 after 100 cycles), while the 1 wt.% FePO4-coated cathode displays the best rate capability (194.3 mAh g−1 at 1 C rate and 167.9 mAh g−1 at 2 C rate). The charge–discharge curves and electrochemical impedance spectra reveal that the improved electrochemical performances are due to the suppression of both the oxygen vacancy elimination at the end of the first charge and side reactions of the cathode with the electrolyte, as well as the decrease in charge transfer polarization by the FePO4 coating layer. [Copyright &y& Elsevier]

In the present work, the electrochemical behaviour of LiFePO4/C electrode has been reported. Specially, the electrochemical impedance spectroscopies (EIS) have been studied in detail. The discharge capacity is more than 120 mAh/g. There are two semicircles being found in the Nyquist plot for the cycled electrode and one semicircle for the as-prepared electrode. It is found that the interface capacitance is in an order of magnitude of 10 μF/cm for the high-frequency semicircle, while for the second semicircle the interface capacitance is 5.3~45.4 × 10 μF/cm. It could be concluded that the high-frequency semicircle is to correspond to the charge transfer process. The function of the carbon layer is also briefly discussed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: A brand new method for synthesizing Mn(PO3(OH))·3H2O is attained in this paper. During this process, pure flake-like Mn(PO3(OH))·3H2O precipitate is prepared using C2H5OH as initiator. Besides that, LiMn0.5Fe0.5PO4/C is successfully synthesized from the Mn(PO3(OH))·3H2O precursor at 650 °C for the first time. Thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) are applied in the characterization of the Mn(PO3(OH))·3H2O precursor and LiMn0.5Fe0.5PO4/C. High-resolution transmission electron microscopy (HRTEM) is also used to investigate the morphology of LiMn0.5Fe0.5PO4/C. X-ray photoelectron spectroscopy (XPS) and galvanostatic charge and discharge test are employed to characterize the Mn(PO3(OH))·3H2O precursor and LiMn0.5Fe0.5PO4 material, respectively. The as-prepared LiMn0.5Fe0.5PO4/C material exhibited a reversible capacity of 131 mAh g−1 at 0.05 C. It can be confirmed that the incorporation of Fe into LiMnPO4 can significantly improve the electrochemical properties for improving the conductivity of the material and facilitating the Li+ diffusion. In addition, a capacity of 120 mAh g−1 is still delivered at 0.05 C rate with a capacity retention of about 91% after 25 cycles, and reversible capacity can reach 105 mAh g−1 at 1 C. [Copyright &y& Elsevier]

Abstract: LiNi1/3Mn1/3Co1/3O2 (NMC) as a cathode material for lithium ion batteries has been synthesized by the sol–gel method. The X-ray diffraction Rietveld refinement results indicated that single-phase NMC with hexagonal layered structure was obtained. Scanning electron microscope images revealed well crystallized NMC with uniform particle size in the range of 100–200 nm. The performance of the NMC electrodes with sodium carboxylmethyl cellulose (CMC), poly(vinylidene fluoride) (PVDF), and alginate from brown algae as binders was compared. Constant current charge–discharge test results demonstrated that the NMC electrode using CMC as binder had the highest rate capability, followed by those using alginate and PVDF binders, respectively. Electrochemical impedance spectroscopy test results showed that the electrode using CMC as the binder had lower charge transfer resistance and lower apparent activation energy than the electrodes using alginate and PVDF as the binders. The apparent activation energies of NMC electrodes using CMC, alginate, and PVDF as binders were calculated to be 27.4 kJ mol−1, 33.7 kJ mol−1, and 36 kJ mol−1, respectively. [Copyright &y& Elsevier]

Abstract: Spherical Li3V2(PO4)3/C (LVP/C) composites are successfully synthesized via two different spray-drying processes. XRD results reveal that some impurities, such as Na3V2(PO4)3, Li2NaV2(PO4)3 and Li4(P2O7), appear when sodium salt of carboxy methyl cellulose (CMC) acts as carbon source. SEM images show two different morphologies: solid spherical particles for LVP/C(A) prepared by adding CMC after pre-sintering, and hollow for LVP/C(B) prepared by adding CMC before pre-sintering. Compared to LVP/C(B), LVP(A) presents higher tap density and better electrochemical performance at any C-rate. Remarkably, another charge/discharge plateaus or anodic/cathodic peaks around 3.85V are detected for both LVP/C(A) and LVP/C(B) electrodes, which is attributed to the formation of Li3−x Na x V2(PO4)3 or some other electrochemically active composites containing Na+. CMC addition sequence has a significant influence on morphology of Li3V2(PO4)3. Furthermore, acting as carbon source and Na dopant, CMC shows a notable effect on electrochemical behavior of Li3V2(PO4)3 cathode material. [Copyright &y& Elsevier]

Abstract: The Li x Ni0.23Co0.12Mn0.65O2 electrode system with various compositions (x =1.19, 1.33, 1.46, 1.58) was synthesized from a metal oxide precursor synthesized by co-precipitation method. The XRD patterns of the prepared powders revealed a hexagonal α-NaFeO2 structure (space group: R-3m, 166) and the existence of a Li2MnO3 phase in the composite structure. In particular, the low Li content sample shows a three integrated structure (spinel, Li2MnO3, LiMO2) for a Li/Metal(Ni/Co/Mn) mol ratio of 1.2. Scanning electron microscopy showed that all the synthesized samples contained spherical agglomerates with a size of 8–10μm. Among the samples tested, Li1.46Ni0.23Co0.12Mn0.65O2 shows relatively high charge and discharge capacity for the first cycle is 287, 192.9mAhg−1, respectively. Also, charge transfer resistance was also significantly improved compare with other samples. [Copyright &y& Elsevier]

Abstract: A life model is developed for a lithium ion cell with a spinel-based cathode. It is assumed in the proposed model that the Mn(III) disproportionation reaction causes the degradation of the spinel cathode. The Mn(III) disproportionation reaction leads to the Mn(II) dissolving into the electrolyte and the formation of an inactive material layer which causes a resistance increase in the cathode. The proposed model is used to investigate the effects of ambient temperature and voltage range of cycling on the loss of the cell capacity and the changes in the volume fraction of the cathode active material, the radius of the cathode particle and the resistance of the cathode. [Copyright &y& Elsevier]

Abstract: Well-formed Li1.131Mn0.504Ni0.243Co0.122O2 cathode materials are synthesized via freeze drying followed by a solid state reaction at temperatures of 750–900 °C. Among these oxides, the one synthesized at 800 °C delivers the highest initial discharge capacity of 246.5 mAh g−1 at 0.1 C (1 C = 200 mA g−1) between 2.5 V and 4.8 V. Enhancing the discharge rate to 1 C, initial capacity of 197.8 mAh g−1 is obtained, and 78.8% capacity is retained after 50 cycles. Furthermore, the diffusion coefficients of Li+ in the lithium-rich layered oxide are about 10−14 cm2 s−1 and 10−15 cm2 s−1 for the initial charge platform at 3.90 V and 4.55 V, respectively, determined by galvanostatic intermittent titration technique (GITT). The Li1.131Mn0.504Ni0.243Co0.122O2 prepared by freeze drying is a promising cathode material for lithium ion batteries. [Copyright &y& Elsevier]

Abstract: CaF2-coated LiMn1/3Ni1/3Co1/3O2 cathode material is prepared via a wet chemical process followed by a solid state reaction. High-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) show that the well coated CaF2 layer has a thickness of 4–8nm, and no interaction of chemical bonding is observed. The CaF2-coated LiMn1/3Ni1/3Co1/3O2 exhibits discharge capacity retention of 98.1% at 0.1C after 50 cycles and high initial discharge capacity of 146.3mAhg−1 at 5C. Furthermore, even at an elevated charge–discharge rate of 5C, capacity retention maintains above 85%. Electrochemical impedance spectroscopy (EIS) shows that the CaF2 coating can stabilize the surface structure and reduce the charge transfer resistance. The CaF2 modification has a promising application in improving the performance of layered oxide cathode materials for Li-ion batteries. [Copyright &y& Elsevier]

Abstract: The cycle performance of spinel LiMn2O4 at 25 and 55°C is improved by LaF3 modification via a chemical deposition method. The physical and electrochemical performances of pristine and LaF3-coated LiMn2O4 cathode materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical measurements. The coated LiMn2O4 with 2.92wt% LaF3 (LaF3-3-LMO) displays capacity retentions of 90.1% and 84.2% at 25 and 55°C, respectively, after 100 cycles, much higher than those of pristine LiMn2O4, 72.7% and 54.8%. The concentration of manganese dissolved from LaF3-3-LMO in electrolyte is much lower than that from pristine LiMn2O4. The analysis of AC impedance indicates that the charge transfer resistance (R ct) and the increase of R ct for LaF3-3-LMO during cycling are much lower than those for pristine LiMn2O4. The significantly improved electrochemical performance of the LaF3-coated LiMn2O4 can be attributed to the reduction of manganese dissolution in electrolyte and charge transfer resistance with the help of LaF3 coating. [Copyright &y& Elsevier]

In this study, Li3V2(1-x)Fe3x(PO4)3 (0 ≤ x ≤ 0.09) powders are prepared via a solution method and heattreated at 700 °C for 8 hours. The chemical composition, morphology, crystalline structure, and valence of iron in the prepared samples were investigated with ICP, SEM, XRD, and EXAFS. The effects of Fe-substitution for vanadium sites on the electrochemical properties as cathode materials for lithium ion batteries are studied with capacity retention study and incremental capacity analysis. In addition to the monoclinic Li3V2(PO4)3 phase, olivine LiFePO4 is also observed when x ≥ 0.03. The valence of iron in the prepared powders is predominately 3+ at low substitution level (x ≤ 0.05), while the ratio of the Fe2+ to Fe3+ increases abruptly when the substitution level is higher than x = 0.07. Among the prepared samples, Li3V1.86Fe0.21(PO4)3 shows the best cycling performance at rates higher than 1C. It demonstrates discharge capacities of 141.2 mAh/g for second cycle and 126 mAh/g after 30 cycles at 5C rate. [ABSTRACT FROM AUTHOR]

The high capacity cathode materials with charge voltage above 4.5 V are widely being developed. To reduce surface reactivity at high voltage, Al2O3 and pullulan are used for coating on the Li(Li0.08Ni0.34Co0.08Mn0.5)O2 surface and are characterized by electrochemical analysis. Charge/discharge and electrochemical results reveal that the organic coating sustains in high voltage cycles. Ionic conductivity of surface coating plays a key role in the battery performance. [ABSTRACT FROM AUTHOR]

Abstract: Promising capacity retention (more than 92% of initial capacity after 100cycles), was exhibited in cells (graphite/xLi2MnO3·yLiMO2) with 2wt.% LiDFOB as additive. The outstanding cell performance was associated with the formation of stable solid electrolyte interface (SEI) film on the surface of electrodes derived from LiDFOB. Compared to the effect of the LiBOB additive, the main reason responsible for the greatly improved durability in LiDFOB added cells might be attributed to the more stable SEI film with lower interfacial resistance on the surface of anode. [Copyright &y& Elsevier]

Abstract: Li3V2(PO4)3/C cathode material was synthesized by using a freeze-drying method followed by carbon-thermal reduction. This as-prepared material has a uniform particle size distribution and a well carbon coating on the surface of Li3V2(PO4)3 particles. The Li3V2(PO4)3/C exhibits good electrochemical performance and cycling stability. Between 3.0 and 4.3V, the composite delivered a reversible capacity of 125.2mAhg−1 at a charge–discharge rate of 1.48C (1C=133mAg−1) and without obviously capacity fading after 100 cycles. Even at 14.8C and 29.6C rates, it can still deliver discharge capacities of 105.6mAhg−1 and 93.3mAhg−1, and the discharge capacities of 84.5 and 60.5mAhg−1 are sustained after 500 cycles, respectively. [Copyright &y& Elsevier]

Abstract: The novel multi-substituted LiNi0.475Al0.01Cr0.04Mn1.475O3.95F0.05 cathode material is synthesized via a sol–gel method. The results show that this material has a well-defined cubic spinel structure, Fd3m space group. The excellent rate capability can be obtained from this material to deliver a discharge capacity of 136.6, 129.0, 119.9, 104.5 and 86.4mAhg−1 at rates of 0.2, 5, 10, 15 and 20C, respectively. It still exhibits satisfactory cycle stability at room temperature (20°C) and elevated temperature (55°C), achieving 128.6 and 129.5mAhg−1 at 1C with the capacity retention of 98% and 99.7% after 100 cycles, respectively. Besides, the favorable rate cycle performance at 55°C has been shown to retain 95.2% of the maximum discharge capacity (102.7mAhg−1) at 10C after 100 cycles. The stable structure, high reversibility and electrochemical reaction kinetics afforded by multiple ions existing in the spinel appear to contribute to the excellent electrochemical performance. [Copyright &y& Elsevier]

Olivine LiFePO/C cathode materials for lithium ion batteries were synthesized using monodisperse polystyrene (PS) nano-spheres and other carbon sources. The structure, morphology, and electrochemical performance of LiFePO/C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge tests, electrochemical impedance spectroscopy (EIS) measurements, and Raman spectroscopy measurements. The results demonstrated that LiFePO/C materials have an ordered olivine-type structure with small particle sizes. Electrochemical analyses showed that the LiFePO/C cathode material synthesized from 7 wt.% PS nano-spheres delivers an initial discharge capacity of 167 mAh g (very close to the theoretical capacity of 170 mAh g) at 0.1 C rate cycled between 2.5 and 4.1 V with excellent capacity retention after 50 cycles. According to Raman spectroscopy and EIS analysis, this composite had a lower I/ I, sp/ sp peak ratio, charge transfer resistance, and a higher exchange current density, indicating an improved electrochemical performance, due to the increased proportion of graphite-like carbon formed during pyrolysis of PS nano-spheres, containing functionalized aromatic groups. [ABSTRACT FROM AUTHOR]

Abstract: The uniform and spherical LiNi0.5Co0.2Mn0.3O2 particles were successfully coated with AlF3. The structures and electrochemical properties of AlF3-coated LiNi0.5Co0.2Mn0.3O2 were characterized by various techniques. When the coating amount was 0.5mol%, the cathode showed enhanced cycling performance and rate capability compared to the pristine LiNi0.5Co0.2Mn0.3O2. The AlF3-coated LiNi0.5Co0.2Mn0.3O2/Li cell had capacity retention of 98% after 100 cycles even at 4C over 2.8–4.5V, while the pristine LiNi0.5Co0.2Mn0.3O2 exhibited capacity retention of only 89%. Moreover, the rate capability and cyclic performance at elevated temperature (55°C) were also improved. Electrochemical impedance spectroscopy testing revealed the improved electrochemical performance, which could be considered that the AlF3 coating layer can suppress the increase of impedance during the charging and discharging process by preventing directly contact of the highly delithiated active material with electrolyte. [Copyright &y& Elsevier]

Abstract: Li3V2(PO4)3/C cathode material is synthesized by a carbon-thermal reduction method using polyvinyl alcohol as carbon source at 700°C. The Li3V2(PO4)3/C electrode presents a high initial discharge capacity of 84.3, 111.1, 128.7, 129.2 and 132.1mAhg−1 at −20, 0, 25, 40 and 65°C between 3.0 and 4.3V, and 118.9, 132.1, 187.6, 180.3 and 172.2mAhg−1 between 3.0 and 4.8V at 0.1C, respectively. However, the electrode only delivers small discharge capacities at −20°C at 10C rate. The capacity fade at low temperatures is mainly attributed to the reduced ionic and electronic conductivity of the electrolyte, the increased impendence of solid electrolyte interface (SEI) and charge-transfer resistance on the electrolyte–electrode interfaces. At higher temperatures, the capacity increases with increasing temperature between 3.0 and 4.3V, but decreases between 3.0 and 4.8V. In the potential range of 3.0–4.8V, the larger crystal structural distortion and non-uniformity of SEI layer at high temperatures may be the main reasons for the capacity loss. [Copyright &y& Elsevier]