Search

Abstract A nanoscale spinel pillaring layer is introduced onto the surface of the LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode material, which is confirmed by combined surface-probing techniques. The functional layer does not change the crystal structure after of pristine LiNi 0.8 Co 0.1 Mn 0.1 O 2 , while it plays a vital role in avoiding unfavorable side reactions occurred in the interphase between cathode materials and electrolyte. The treated sample shows suppressed capacity decay (19.3%) as compared to the pristine sample (41.9%) after 200 cycles at 2 C rate. Moreover, it can also improve the storage performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 by restraining the generation of Li 2 CO 3 and the NiO-like phase during the storage process in humid air. Thus, the capacity retention capability is improved after storage in air for 2 months, which improves from 52.2% to 77.6% after 200 cycles. Overall, this study offers an effective solution to improve the cyclability and storage stability of the Ni-based cathode materials. Highlights • A spinel pillaring layer is introduced onto the surface of the Ni-based materials. • The spinel pillaring layer can alleviate HF erosion, and side reactions between electrode and electrolyte. • The spinel pillaring layer can suppress the reduction of nickel and the generation of Li 2 CO 3. • Both cycle performance and storage property are enhanced. [ABSTRACT FROM AUTHOR]

To improve the stability of LiVPO 4 F electrode/electrolyte interface, Li 3 PO 4 is used to modify LiVPO 4 F composite (P-LVPF) for the first time. Morphological characterization shows that LiVPO 4 F particles are wrapped by amorphous carbon and lithium ionic conductor Li 3 PO 4 as the interlayer and outer layer, respectively. Compared to the pristine sample, the resultant P-LVPF exhibits greatly improved rate capability and elevated-temperature cycle performance when applied as the cathode material for lithium ion batteries. Specifically, the Li 3 PO 4 modified sample specific capacity maintains 77.6% at 1 C after 100 cycles under 55 °C. Such improvement is attributed to the fact that the Li 3 PO 4 coating layer not only acts as a good ionic conductor for LiVPO 4 F, but also serves as a physical barrier between electrode and electrolyte which can build a stable interface. [ABSTRACT FROM AUTHOR]

The chemical diffusion coefficients of lithium ion ( $$ {D}_{{\mathrm{Li}}^{+}} $$) in LiVPOF (0 ≤ x ≤ 2) between 3.0 and 0.01 V are systematically analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT). The results indicate that the $$ {D}_{{\mathrm{Li}}^{+}} $$ values depend heavily on the voltage state. Based on the results from EIS and GITT, the diffusion coefficients ( $$ {D}_{{\mathrm{Li}}^{+}} $$) measured in a single-phase region below 1.7 V have relatively steady values of about 10 (EIS) and 10 (GITT) cm s, respectively, while the $$ {D}_{{\mathrm{Li}}^{+}} $$ values in the single-phase region above 1.9 V decrease rapidly from 10 to 10 cm s due to concentration of lithium ions in the bulk LiVPOF. The Li chemical diffusion coefficients measured in the two-phase region by GITT range a lot from 10 to 10 cm s, while the $$ {D}_{{\mathrm{Li}}^{+}} $$ values in the two-phase region determined by CV are around 10 cm s. By the GITT, the $$ {D}_{{\mathrm{Li}}^{+}} $$ values in the two-phase region vary in non-linear shape with the charge-discharge voltage, which is ascribed to strong interactions of Li with other ions. [ABSTRACT FROM AUTHOR]

Abstract: Carbon coated triclinic LiVPO4F samples are synthesized by annealing the precursor obtained through a soft chemical route with mechanical activation assist. The V(+5) is reduced to V(+3) by oxalic acid dehydrate during ball milling process, and green slurry of amorphous Li–V–PO4–F is obtained. When the temperature rises to 550°C, the precursor starts crystallizing and good crystal of pure-phase LiVPO4F can be obtained at 550–650°C. But Li3V2(PO4)3 impurity is observed in samples fired at temperature above 700°C because of the volatilization of HF gas in the presence of moisture at high temperature. Charge–discharge tests show that the sample sintered at 700°C exhibits the best electrochemical performance, delivering the initial discharge capacity of 136 at 0.1C rate and 123mAhg−1 at 1C rate. Even at 5C rate, the discharge capacity remains 107mAhg−1 and keeps 95.3% after 100 cycles. EIS analysis shows that it possesses smaller impedance than other samples. The apparent chemical coefficient of lithium ions in the prepared sample is evaluated by cyclic voltammetry. [Copyright &y& Elsevier]

Abstract: Spherical LiNi0.8Co0.1Mn0.1O2 materials have been synthesized by hydroxide co-precipitation method. Layered oxyfluoride LiNi0.8Co0.1Mn0.1O2− z F z (0≤ z ≤0.06) cathodes have been synthesized by firing NH4F with LiNi0.8Co0.1Mn0.1O2 oxides at the relatively low temperature of 450°C. The effect of fluorine content on the structure, morphology and electrochemical performance of the LiNi0.8Co0.1Mn0.1O2− z F z has been extensively studied. The results indicated that the initial discharge capacity slightly decreased with the increase in the content of fluorine substitution. However, cycling performance and rate capability were improved by the fluorine substitution. Capacity retentions after 100cycles at room temperature were 79.7% for z =0, 94.3% for z =0.02, 91.5% for z =0.04, and 86.9% for z =0.06. In addition, after being stored at 90°C for 5h in a fully charged state, fluorine substituted LiNi0.8Co0.1Mn0.1O2 exhibited better cycling performance than pristine LiNi0.8Co0.1Mn0.1O2. Overall, fluorine substitution was an effective way to improve electrochemical performance. [Copyright &y& Elsevier]

Abstract α-MoO 3 coated Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 electrode materials were obtained via a simple and effective wet chemical method. The results of X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS) indicated that α-MoO 3 had been successfully coated on the surface of pristine materials. Charge-discharge measurements demonstrated that the α-MoO 3 thin layer could enhance the electrochemical performances. The initial coulombic efficiency improved from 75.7% to 89.6%, and the modified sample exhibited good cyclic performance of 87.0% at 100 mA g−1 after 100 cycles and 85.3% at 200 mA g−1 after 100 cycles with the excellent discharge properties. According to the analysis of electrochemical impedance spectroscopy (EIS) and cyclic voltammogram (CV), the largely enhanced electrochemical performance are mainly due to the restrain of the side reactions between electrode and electrolyte and the increased migration rate of Li+ between the electrode/electrolyte interface by α-MoO 3 film. Highlights • α-MoO 3 -coated sample shows significantly improved initial coulombic efficiency. • A Li+-free insertion host, α-MoO 3 , is coated on Li-rich Mn-based electrode material. • Superior cyclic performance and rate capability are obtained after Mo coating. • The mechanisms of Mo composites coating layer on improved performances are discussed in detail. [ABSTRACT FROM AUTHOR]

In order to improve the rate capability and mitigate the voltage decay of lithium rich layered oxides, chromium doped cathode materials Li 1.2 [Mn 0.54 Ni 0.13 Co 0.13 ] 1−x Cr x O 2 (x = 0,0.003,0.005,0.007) is synthesized via co-precipitation method followed by calcination. As a result, Cr-doped samples present shortened voltage platform at 4.5 V, indicating that the escape of lattice oxygen is suppressed by Cr doping. Among all samples, Li 1.2 [Mn 0.54 Ni 0.13 Co 0.13 ] 1−x Cr x O 2 (x = 0.005) sample shows the greatest rate capability (119.3 mAh g −1 at 10 C) and the minimum voltage drop (0.6167 V) after 200 cycles at 1.0 C. The reasons for the improved electrochemical performance are the enhanced structural stability, the stronger Cr O bond than Mn O band and the decreased metal–oxygen covalency induced by Cr doping. [ABSTRACT FROM AUTHOR]

Molybdenum doping is introduced to improve the electrochemical performance of lithium-rich manganese-based cathode material. X-ray diffraction (XRD) results illustrate that the crystallographic parameters a , c and lattice volume V become larger with the increase of Mo content. The scanning electron microscope (SEM) shows that the molybdenum substitution increases the crystallinity of the primary particles. When evaluated as cathode material, the as-prepared Li[Li 0.2 Mn 0.54- x /3 Ni 0.13- x /3 Co 0.13- x /3 Mo x ]O 2 ( x = 0.007) delivers a discharge capacity of 155.5 mA h g −1 at 5 C (1 C = 250 mA g −1 ) and exhibits the capacity retention of 81.8% at 1 C after 200 cycles. The results of cyclic voltammetry (CV) and electronic impedance spectroscopy (EIS) tests reflect that the molybdenum substitution is able to significantly reduce the electrode polarization and lower the charge-transfer resistance. Within appropriate amount of Mo doping, the lithium ion diffusion coefficient of the material can reach to 8.92 × 10 –15 cm 2 s −1 , which is ~ 30 times higher than that of pristine materials (2.65 × 10 –16 cm 2 s −1 ). [ABSTRACT FROM AUTHOR]

[Display omitted] • 0.5 M Pyr1(10)TFSI is introduced as a non-consuming electrolyte additive and uniform lithium deposition by electrostatic shielding mechanism. • The adsorption of Pyr1(10)+ cation is explored by Surface-enhanced Raman spectroscopy and EIS. • Outstanding cyclability is demonstrated in LiFePO 4 ||Li full cells with low N/P radio. Lithium (Li) metal anodes have attracted much attention as their high specific capacity and low electrochemical potential significantly boost the energy density of secondary batteries. Nonetheless, the uncontrolled growth of Li dendrites causing a poor cycle capability restricts the commercialization of Li metal batteries. Herein, an ionic liquid with a long aliphatic chain (N-methyl-N-decyl pyrrolidinium (Pyr1(10)+) bis(trifluoromethanesulphonyl)imide (TFSI−)) is introduced as a non-consuming electrostatic shielding additive into the ether-based electrolyte. The admirable compatibility of Pyr1(10)+ cation with Li metal is verified via electrochemical analysis, and the adsorption of Pyr1(10)+ on the Li-metal/electrolyte interface is confirmed by Surface-enhanced Raman spectroscopy technique. Through redistributing the Li ions on the surface of Li metal, the growth of Li dendrites is suppressed, so as to improve the cycling performance of Li metal anodes in symmetric cells, asymmetric cells and Li||LiFePO 4 full cells with low N/P ratio (3:1). This study provides new insights into revealing the electrostatic shielding mechanism of regulating Li metal deposition and prolonging the long-term cycling. [ABSTRACT FROM AUTHOR]

To improve the electrochemical performance of LiVPO 4 F at room and elevated temperature focusing on the stability of LiVPO 4 F electrode/electrolyte interface, for the first time, MoS 2 nanosheets are introduced to modify LiVPO 4 F/C composites. The coating of MoS 2 layers on the surface of LiVPO 4 F/C nanoparticles is realized via a solution method followed by low-temperature calcination. Morphological observations present that the MoS 2 sheets are homogeneously wrapped around the LiVPO 4 F/C particles. When employed as cathode materials for lithium ion batteries, the MoS 2 -modified LiVPO 4 F/C composites exhibit superior high-rate capability and greatly improved cycle ability compared to bare one, and the sample coated with 1.75 wt% MoS 2 (2M-LVPF) delivers the best electrochemical performance. In particular, it maintains the capacity retention of 91.7% in 100 cycles at 2.0C and delivers a reversible specific capacity of 112 mAh g −1 at a high rate of 8.0C under room temperature. More importantly, it shows greatly improved cycling stability at elevated temperature (55 °C), maintaining 88.1% of its initial capacity at 0.5C after 50 cycles. The reasons for such improvement lie in the MoS 2 coating layer acting as a physical barrier between electrode and electrolyte, as well as electronic/ionic conducting framework for LiVPO 4 F particles. [ABSTRACT FROM AUTHOR]

Abstract: LiCoO2 is successfully coated with oxyfluoride ZrO x F y by a chemical deposition method for the first time. The formation of a uniform coating layer on the surface of the cathode particles is confirmed by SEM, TEM, EDX and XPS. The coated sample maintains the pristine layered structure according to the XRD result. Compared with pristine LiCoO2, the ZrO x F y -coated sample exhibits enhanced electrochemical performance especially at high cutoff voltage. Similar discharge capacities are delivered by both pristine and coated samples in various voltage ranges. However, the coated sample shows improved cycling performance, maintaining 56.4%, 32.8% capacity retention after 200 cycles, which is much more than 30.3%, 10.5% that is shown by the pristine sample in the voltage range of 3.0–4.5V and 3.0–4.6V, respectively. [Copyright &y& Elsevier]

Abstract: The degradation of Ni-rich LiNi0.8Co0.15Al0.05O2 cathode material is successfully suppressed via a facile in situ oxidizing-coating method. KMnO4 is used as not only a Mn source but also an oxidant. X-ray diffraction (XRD) and scanning electron microscope (SEM) results demonstrate that the structure and morphology of the KMnO4-pretreated sample are the same as the pristine one. X-ray photoelectron spectroscopy (XPS) confirms that the valence state of Mn is +4 and the Ni3+ ions are partly reduced to Ni2+ when the material is doped with Mn4+. Besides, the Mn4+ ions are proved to distribute uniformly on the surface of the materials particles through energy dispersive spectrometer (EDS) and EDS elemental mapping. And it is confirmed that the concentration of Ni in the outer layer is reduced by the Mn-surface-modification. From the electrochemical characterizations, it is confirmed that the presence of tetravalent Mn at the surface can suppress the capacity fading during charge–discharge cycles, even under elevated temperature and overcharge conditions, and can prevent the material from deterioration during storage in air. [Copyright &y& Elsevier]

Abstract: Graphene-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 is synthesized by the spray drying method. The morphology and electrochemical performances of the pristine and graphene-coated cathodes have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), charge–discharge measurements, as well as Ac impedance spectroscopy. At 250mAg−1, the pristine and graphene-coated samples deliver capacities of ∼141 and 153mAhg−1 with capacity retention of 80 and 97% in 50 cycles, respectively. An analysis of the charge–discharge capacity values and electrochemical impedance spectroscopy (EIS) measurements reveal that the improved electrochemical performances of the graphene-coated sample are due to the suppression of the solid–electrolyte interfacial (SEI) layer and the enhancement of surface electronic conductivity. [Copyright &y& Elsevier]

Abstract: The effect of water washing on LiNi0.8Co0.1Mn0.1O2 cathode is extensively studied with respect to the electrochemical properties, structural stabilities, and storage characteristics. Water washing can improve the cycling performance and structural stability of LiNi0.8Co0.1Mn0.1O2 material in electrolyte, although with a slight deleterious effect on the capacity. Storage tests of the 4.3 V charged electrodes at 90 °C after 30 days show that Ni, Co, Mn in fresh and washed samples are dissolved in electrolyte, but the amount of dissolved Ni4+ ions after washing decreases by 31.5% compared with the fresh cathode. Moreover, the fresh sample transforms into the spinel phase with a Fd3m space group, whereas the washed sample remains as a layered hexagonal phase with an Rm space group. FTIR spectroscopy, transmission electron microscope (TEM), X-ray diffraction (XRD) and electrochemical studies indicate that the washed materials become more easily attached upon exposure to air, accompanied by significant increase in cationic disorder and NiO-like cubic phase near surface. [Copyright &y& Elsevier]