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1.
In order to establish the mechanism and to determine the parameters of lithium transport in electrodes based on lithium-vanadium phosphate (Li3V2(PO4)3), the kinetic model was designed and experimentally tested for joint analysis of electrochemical impedance (EIS), cyclic voltammetry (CV), pulse chronoamperometry (PITT), and chronopotentiometry (GITT) data. It comprises the stages of sequential lithium-ion transfer in the surface layer and the bulk of electrode material’s particles, including accumulation of lithium in the bulk. Transfer processes at both sites are of diffusion nature and differ significantly, both by temporal (characteristic time, τ) and kinetic (diffusion coefficient, D) constants. PITT data analysis provided the following D values for the predominantly lithiated and delithiated forms of the intercalation material: 10?9 and 3 × 10?10 cm2 s?1, respectively, for transfer in the bulk and 10?12 cm2 s?1 for transfer in the thin surface layer of material’s particles. D values extracted from GITT data are in consistency with those obtained from PITT: 3.5–5.8 × 10?10 and 0.9–5 × 10?10 cm2 s?1 (for the current and currentless mode, respectively). The D values obtained from EIS data were 5.5 × 10?10 cm2 s?1 for lithiated (at a potential of 3.5 V) and 2.3 × 10?9 cm2 s?1 for delithiated (at a potential 4.1 V) forms. CV evaluation gave close results: 3 × 10?11 cm2 s?1 for anodic and 3.4 × 10?11 cm2 s?1 for cathodic processes, respectively. The use of complex experimental measurement procedure for combined application of the EIS, PITT, and GITT methods allowed to obtain thermodynamic E,c dependence of Li3V2(PO4)3 electrode, which is not affected by polarization and heterogeneity of lithium concentration in the intercalate.  相似文献   

2.
A cathode material, 0.5Li2MnO3 0.5LiNi0.5Mn0.5O2, was prepared by citric acid-assisted sol–gel method and its electrochemical performance was investigated. It delivered a charge capacity of 270 mAh g?1 and a discharge capacity of 189 mAh g?1 in the first cycle. With the increase of current density from 14 to 28 mA g?1, the discharge capacity dropped severely to 130 mA g?1. Obviously, the rate capability of the material was inferior to most of the oxide cathode materials. The diffusion coefficient of this material was calculated to be 6.04?×?10?12 cm2 s?1 from the results of cyclic voltammetry measurements. Moreover, diffusion coefficients between 3.13?×?10?12 and 1.22?×?10?10 cm2 s?1 in the voltage range of 3.8–4.7 V were obtained by capacity intermittent titration technique. This, together with the localized Li2MnO3 domains in the crystal structure, may validate the poor rate capability.  相似文献   

3.
Titanium dioxide (TiO2)-based materials have been well studied because of the high safety and excellent cycling performance when employed as anode materials for lithium ion batteries (LIBs), whereas, the relatively low theoretical capacity (only 335 mAh g?1) and serious kinetic problems such as poor electrical conductivity (~?10?13S cm?1) and low lithium diffusion coefficient (~?10?9 to 10?13 cm2 s?1) hinder the development of the TiO2-based anode materials. To overcome these drawbacks, we present a facile strategy to synthesize N/S dual-doping carbon framework anchored with TiO2 nanoparticles (NSC@TiO2) as LIBs anode. Typically, TiO2 nanoparticles are anchored into the porous graphene-based sheets with N, S dual doping feature, which is produced by carbonization and KOH activation process. The as-obtained NSC@TiO2 electrode exhibits a high specific capacity of 250 mAh g?1 with a coulombic efficiency of 99% after 500 cycles at 200 mA g?1 and excellent rate performance, indicating its promising as anode material for LIBs.  相似文献   

4.
Qun Wu  Yanhui Xu  Hua Ju 《Ionics》2013,19(3):471-475
In the present work, a new-type low-cost lithium ion battery cathode material, the Mikasaite-type iron sulfate, has been studied. It can be prepared by heating the water-containing iron sulfate raw chemicals in air atmosphere. The experimental results have shown that the oxidation and the reduction peaks are 3.92 and 3.37 V in the cyclic voltammogram, respectively, when the scanning rate is 0.05 mV s?1. The galvanostatic measurements have explored that the voltage plateau during charging is slightly less than 3.70 V and the discharge voltage plateau is 3.40 V for the first cycle and 3.50 V for the following cycles at 0.1 C rate. The discharge capacity in the first cycle can reach 116 mAh g?1, about 87 % of the theoretical capacity (134 mAh g?1). It is believed that the product in the fully discharged state is Li2Fe2(SO4)3. However, the insertion reaction is reversible only for the second lithium ion. During cycling, the reversible capacity remains about 60 mAh g?1. Further capacity fade is not found in the 20 discharge–charge cycles. The electrochemical impedance measurements have shown that there are two compressed semicircles in the Nyquist plots and a Warburg impedance in the low-frequency domain. The high-frequency semicircle is related with the electrode’s structural factor and the intermediate-frequency semicircle corresponds to the charge-transfer process.  相似文献   

5.
High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~?200 °C), ionic conductivity (6.42?×?10?4 S cm?1), lithium ion conductivity (1.40?×?10?4 S cm?1 at 30 °C), and wide electrochemical stability window (~?4.10 V versus Li/Li+ at 30 °C). Furthermore, the surface of LiFePO4 cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO4 cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO4. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g?1 for graphene oxide-coated LiFePO4 and without coated LiFePO4 at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO4 cathode after coating with graphene oxide.  相似文献   

6.
Nitrogen-doped carbon nanofiber (NCNF) decorated LiFePO4 (LFP) composites are synthesized via an in situ hydrothermal growth method. Electrochemical performance results show that the embedded NCNF can improve electron and ion transfer, thereby resulting in excellent cycling performance. The as-prepared LFP and NCNF composites exhibit excellent electrochemical properties with discharge capacities of 188.9 mAh g?1 (at 0.2 C) maintained at 167.9 mAh g?1 even after 200 charge/discharge cycles. The electrode also presents a good rate capability of 10 C and a reversible specific capacity as high as 95.7 mAh g?1. LFP composites are a potential alternative high-performing anode material for lithium ion batteries.  相似文献   

7.
A series of Li3V2(PO4)3/C composite cathodes have been prepared by the organic solvent replacement drying method. Five kinds of organic solvent including ethyl alcohol, butyl alcohol, 2-methoxyethanol, 1,2-propylene glycol, and ethylene glycol were used in the drying process to replace the water respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests were employed to analyze the crystal structure, morphology, and electrochemical properties of the as-prepared materials. The results show that the organic solvent has a great influence on the secondary particle size of the as-synthesized materials. Special emphasis is placed on the sample prepared with 1,2-propylene glycol, which has the smallest average particle size and uniform distribution, thus leading to the best high rate performance and long-term cycling stability. The electrode exhibits average specific discharge capacities of 127.6, 128.3, 127.7, 126.7, 125.5, 124.4, 121.9, and 117.0 mAh g?1 at 0.1, 0.2, 0.5, 1, 3, 5, 10, and 20C, respectively. More encouragingly, this sample delivers an outstanding cycle life with capacity retention of up to 94.68% even after 1000 cycles at 20C. Moreover, EIS results demonstrate that this sample has the minimum resistance and the largest apparent lithium ion diffusion coefficient (1.569 × 10?7 cm2 s?1) which can facilitate to the Li+ diffusion during the charge/discharge process. Our results indicate that this preparation strategy can be facile and versatile for the synthesis of other high-rate and high-capacity intercalation materials.  相似文献   

8.
The influence of post-calcination treatment on spinel Li4Ti5O12 anode material is extensively studied combining with a ball-milling-assisted rheological phase reaction method. The post-calcinated Li4Ti5O12 shows a well distribution with expanded gaps between particles, which are beneficial for lithium ion mobility. Electrochemical results exhibit that the post-calcinated Li4Ti5O12 delivers an improved specific capacity and rate capability. A high discharge capacity of 172.9 mAh g?1 and a reversible charge capacity of 171.1 mAh g?1 can be achieved at 1 C rate, which are very close to its theoretical capacity (175 mAh g?1). Even at the rate of 20 C, the post-calcinated Li4Ti5O12 still delivers a quite high charge capacity of 124.5 mAh g?1 after 50 cycles, which is much improved over that (43.9 mAh g?1) of the pure Li4Ti5O12 without post-calcination treatment. This excellent electrochemical performance should be ascribed to the post-calcination process, which can greatly improve the lithium ion diffusion coefficient and further enhance the electrochemical kinetics significantly.  相似文献   

9.
A facile two-step approach has been used for the synthesis of porous SnO2 rods: the initial room-temperature precipitation of precursor SnC2O4 and its subsequent thermal decomposition at 550 °C. Both the as-obtained porous SnO2 microrods (length ~10.0?±?3.5 μm, diameter ~1.1?±?0.4 μm) and submicrorods (length ~5.8?±?1.9 μm, diameter ~0.4?±?0.1 μm) are the crystalline mixtures of major tetragonal and minor orthorhombic crystal phases, showing a tetragonal fraction of 84.7 and 87.0 %, respectively. When applied as a lithium-ion battery anode, the porous submicrorods (specific surface area ~13.6 m2 g?1) can deliver an initial discharge capacity of 1,730.7 mAh g?1 with a high coulombic efficiency of 61.6 % and show the 50th discharge capacity of 662.8 mAh g?1 at 160 mA g?1 within a narrow potential range of 10.0 mV to 2.0 V. Similarly, even the anode of porous microrods (specific surface area ~11.8 m2 g?1) can still exhibit an initial discharge capacity of 1,661.1 mAh g?1 at 160 mA g?1 with a coulombic efficiency of 60.9 %. Regardless of the polymorphic nature, the acquired porosity may only alleviate the huge volume change of anodes for the first cycle; thus, the structural parameters of average size and specific surface area can be feasibly associated with the enhanced lithium storage capability. Anyway, these indicate a facile oxalate precursor method for the controlling synthesis and high performance of rodlike SnO2 for lithium-ion batteries.  相似文献   

10.
A commercial carbon black with microporous framework is used as carbon matrix to prepare sulfur/microporous carbon (S/MC) composites for the cathode of lithium sulfur (Li-S) battery. The S/MC composites with 50, 60, and 72 wt.% sulfur loading are prepared by a facile heat treatment method. Electrochemical performance of the as-prepared S/MC composites are measured by galvanostatic charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), with carbonate-based electrolyte of 1.0 M LiPF6/(PC-EC-DEC). The composite with 50 wt.% sulfur presents the optimized electrochemical performance, including the utilization of active sulfur, discharge capacity, and cycling stability. At the current density of 50 mA g?1, it can demonstrate a high initial discharge capacity of 1624.5 mAh g?1. Even at the current density of 800 mA g?1, the initial capacity of 1288.6 mAh g?1 can be obtained, and the capacity can still maintain at 522.8 mAh g?1 after 180 cycles. The remarkably improved electrochemical performance of the S/MC composite with 50 wt.% sulfur are attributed to the carbon matrix with microporous structure, which can effectively enhance the electrical conductivity of the sulfur cathode, suppress the loss of active material during charge/discharge processes, and restrain the migration of polysulfide ions to the lithium anode.  相似文献   

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