Facile synthesis of N-doped carbon-coated Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode for application in high-rate lithium ion batteries

A facile sol-gel approach for the synthesis of lithium titanate composite decorated with N-doped carbon material (LTO/NC) is proposed. Urea is used as a nitrogen source in the proposed approach. The LTO/NC exhibits superior electrochemical performances as an electrode material for lithium-ion batteries, delivering a discharge capacity of as high as 103 mAh g^?1 at a high rate of 20 C and retaining a stable reversible capacity of 90 mAh g^?1 after 1000 cycles, corresponding to 100% capacity retention. These excellent electrochemical performances are proved by the nanoscale structure and N-doped carbon coating. NC layers were uniformly dispersed on the surface of LTO, thus preventing agglomeration, favoring the rapid migration of the inserted Li ion, and increasing the Li⁺ diffusion coefficient and electronic conductivity. LTO with the appropriate amount of NC coating is a promising anode material with applications in the development of high-powered and durable lithium-ion batteries.     

A novel method to synthesize SnP<Subscript>2</Subscript>O<Subscript>7</Subscript> spherical particles for lithium-ion battery anode

For the urgent demand of higher capacity of lithium-ion battery anode, tin pyrophosphate has attracted more and more attention because of its high theoretical capacity, cheapness, and no toxicity. However, production of stable mesoporous sphere structure and improvement of electrochemical performance remain a challenge. Here, SnP₂O₇ spherical particles were successfully prepared through spray drying method with SnCl₄·5H₂O and C₂H₈O₇P₂. Crystallization and microstructure were investigated by TG-DSC, XRD, SEM, and TEM. With the obtained mesoporous SnP₂O₇ particles after carbon coating, it demonstrates a high initial capacity reaching up to 1218 mAh g^?1 and a significantly stable cycling performance with 620 mAh g^?1 after 80 deep electrochemical cycles.     

Enhancing battery performance by nano Si addition to Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> as anode material on lithium-ion battery

The lithium-ion battery is a battery that is being developed to become a repository of energy, particularly for electric vehicles. Lithium titanate (Li₄Ti₅O₁₂) anodes are quite promising for this application because of its zero-strain properties so it can withstand the high rate. However, the capacity of LTO (Li₄Ti₅O₁₂) is still relatively low. Therefore, the LTO needs to be combined with other materials that have high capacity such as Si. Silicon has a very high capacity which is 4200 mAh/g, but it has a high volume of the expansion. Nano-size can also help increase the capacity. Therefore composite of LTO/nano Si is made to create an anode with a high capacity and also stability. Nano Si is added with a variation of 1, 5, and 10%. LTO/nano Si composite is characterized using XRD, SEM-EDX, and TEM-EDX. Then, to determine the battery performance, EIS, CV, and CD tests were conducted. From those tests, it is studied that Si improves the conductivity of the anode, but not significantly. The addition of Si results a greater battery capacity which is 262.54 mAh/g in the LTO-10% Si. Stability of composite LTO/nano Si is good, evidenced by the coulomb efficiency at the high rate of close to 100%.     

Improved electrochemical performance of Li<Subscript>1.2</Subscript>Ni<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>O<Subscript>2</Subscript> cathode material with fast ionic conductor Li<Subscript>3</Subscript>VO<Subscript>4</Subscript> coating

Layered lithium-enriched nickel manganese oxides Li_1.2Ni_0.2Mn_0.6O₂ have been synthesized and coated by fast ionic conductor Li₃VO₄ with varying amounts (1, 3, and 5 wt%) in this paper. The effect of Li₃VO₄ on the physical and electrochemical properties of Li_1.2Ni_0.2Mn_0.6O₂ has been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), discharge, cyclic performance, rate capability, and electrochemical impedance spectroscopy (EIS). The discharge capacity and coulomb efficiency of Li_1.2Ni_0.2Mn_0.6O₂ in the first cycle have been improved after Li₃VO₄ coating. And, the 3 wt% Li₃VO₄-coated Li_1.2Ni_0.2Mn_0.6O₂ shows the best discharge capacity (246.8 mAh g^?1), capacity retention (97.3 % for 50 cycles), and rate capability (90.4 mAh g^?1 at 10 C). Electrochemical impedance spectroscopy (EIS) results show that the R _ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode decreases after Li₃VO₄ coating, which is due to high lithium ion diffusion coefficient of Li₃VO₄, is responsible for superior rate capability.     

Synthesis and lithium-ion storage performances of LiFe<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>PO<Subscript>4</Subscript>/C nanoplatelets and nanorods

Carbon-coated olivine-structured LiFe_0.5Co_0.5PO₄ solid solution was synthesized by a facile rheological phase method and applied as cathode materials of lithium-ion batteries. The nanostructure’s properties, such as morphology, component, and crystal structure for the samples, characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett, and Teller (BET) determination, X-ray photoelectron spectroscopy (XPS), and the electrochemical performances were evaluated using constant current charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results indicate that nanoplatelet- and nanorod-structured LiFe_0.5Co_0.5PO₄/C composites were separately obtained using stearic acid or polyethylene glycol 400 (PEG400) as carbon source, and the surfaces of particles for the two samples are ideally covered by full and uniform carbon layer, which is beneficial to improving the electrochemical behaviors. Electrochemical tests verify that the nanoplatelet LiFe_0.5Co_0.5PO₄/C shows a better capacity capability, delivering a discharge specific capacity of 133.8, 112.1, 98.3, and 74.4 mAh g^?1 at 0.1, 0.5, 1, and 5 C rate (1 C?=?150 mA g^?1); the corresponding cycle number is 5th, 11th, 15th, 20th, and 30th, respectively, whereas the nanorod one possesses more excellent cycling ability, with a discharge capacity of 83.3 mAh g^?1 and capacity retention of 86.9% still maintained after cycling for 100 cycles at 0.5 C. Results from the present study demonstrate that the LiFe_0.5Co_0.5PO₄ solid solution nanomaterials with favorable carbon coating effect combine the characteristics and advantage of LiFePO₄ and LiCoPO₄, thus displaying a tremendous potential as cathode of lithium-ion battery.     

Acacia gum-assisted co-precipitating synthesis of LiNi<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>O<Subscript>2</Subscript> cathode material for lithium ion batteries

LiNi_0.5Co_0.2Mn_0.3O₂ particles of uniform size were prepared through carbonate co-precipitation method with acacia gum. The precursor of carbonate mixture was calcined at 800 °C, and a well-crystallized Ni-rich layered oxide was got. The phase structure and morphology were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The micro-sized particles delivered high initial discharge capacity of 164.3 mA h g^?1 at 0.5 C (1 C?=?200 mA g^?1) between 2.5 and 4.3 V with capacity retention of 87.5 % after 100 cycles. High reversible discharge capacities of 172.4 and 131.4 mA h g^?1 were obtained at current density of 0.1 and 5 C, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed to further study the LiNi_0.5Co_0.2Mn_0.3O₂ particles. Anyway, the excellent electrochemical performances of LiNi_0.5Co_0.2Mn_0.3O₂ sample should be attributed to the use of acacia gum.     

Study on electrochemical performance of Mg-doped Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript> cathode material for Li-ion batteries

In this paper, Li₂Fe_1?yMg_ySiO₄/C (y?=?0, 0.01, 0.02, 0.03, 0.05), a cathode material for lithium-ion battery was synthesized by solid-state method and modified by doping Mg²⁺ on the iron site. The effects of Mg²⁺ doping on the crystal structure and electrochemical performance Li₂FeSiO₄ was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical tests. Electrochemical methods of measurement were applied including constant current charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), to determine the electrochemical performance of the material and the optimal doping ion and ratio. The results showed that Li₂Fe_0.98Mg_0.02SiO₄/C has the higher specific capacity and better cycle stability as well as lower impedance and better reversibility. The enhanced electrochemical performance can be attributed to the increased electronic conductivity, the decreased charge transfer impedance, and the improved Li-ion diffusion coefficient. Then, further study on the synthesis conditions was performed to find the optimal combustion temperature and time. According to the study, the material which has the best electrochemical performance, shows initial discharge specific capacity of 142.3 mAh g^?1 at 0.1 C (1 C?=?166 mA g^?1) and coulomb efficiency of 95.6%, under the condition that the temperature is 700 °C and the calcining time is 10 h.     

ZnO-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material for lithium-ion batteries synthesized by a combustion method

ZnO-coated LiMn₂O₄ cathode materials were prepared by a combustion method using glucose as fuel. The phase structures, size of particles, morphology, and electrochemical performance of pristine and ZnO-coated LiMn₂O₄ powders are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy (XPS). XRD patterns indicated that surface-modified ZnO have no obvious effect on the bulk structure of the LiMn₂O₄. TEM and XPS proved ZnO formation on the surface of the LiMn₂O₄ particles. Galvanostatic charge/discharge test and rate performance showed that the ZnO coating could improve the capacity and cycling performance of LiMn₂O₄. The 2 wt% ZnO-coated LiMn₂O₄ sample exhibited an initial discharge capacity of 112.8 mAh g^?1 with a capacity retention of 84.1 % after 500 cycles at 0.5 C. Besides, a good rate capability at different current densities from 0.5 to 5.0 C can be acquired. CV and EIS measurements showed that the ZnO coating effectively reduced the impacts of polarization and charge transfer resistance upon cycling.     

Influence of co-precipitation temperature on microstructure and electrochemical properties of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript> cathode materials for lithium ion batteries

The layered Li-rich Mn-based cathode materials Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ were prepared by using co-precipitation technique at different temperatures, and their crystal microstructure and particle morphology were observed and analyzed by XRD and SEM. The electrochemical properties of these samples were investigated by using charge-discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results indicated that all samples are of high purity. When the precursors were co-precipitated at 50 °C, their cathode materials have the most uniform and full particles and exhibit the highest initial discharge capacity (289.4 mAh/g at 0.1C), the best cycle stability (capacity retention rate of 91.2 % after 100 cycles at 0.5C), and the best rate performance. The EIS results show that the lower charge transfer resistance of 50 °C sample is responsible for its superior discharge capacity and rate performance.     

Effect of high-temperature crystallization on the electrochemical properties of LiNi<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>O<Subscript>2</Subscript> synthesized from a lithiated transition metal oxide precursor

The lithiated transition metal oxide precursor (LNCMO) with typical α-NaFeO₂ structure and imperfect crystallinity, obtained from a hydrothermal process, was pretreated at 500 °C and then subjected to sintering at 800–920 °C to synthesize the ternary layered LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523). X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge testing were used for investigating the effect of the high-temperature crystallization on the properties of the NCM523 cathode materials. The results show that the materials heated at 880–900 °C possess superior cation ordering, perfect crystallinity, and excellent electrochemical performances, among which the material heated at 900 °C delivers better performances, with the initial discharge capacity of 152.6 mAh g^?1 at 0.5 C over 3.0 to 4.3 V and the capacity retention of 95.5% after 50 cycles. Furthermore, the effect of the high-temperature crystallization on the Li⁺ diffusion coefficient, potential polarization, and electrochemical resistance are discussed.     

Pr-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> nanofibers as an anode material for lithium-ion batteries with outstanding cycling performance and rate performance

Pr-doped Li₄Ti₅O₁₂ in the form of Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0, 0.01, 0.03, 0.05, and 0.07) was synthesized successfully by an electrospinning technique. ICP shows that the doped samples are closed to the targeted samples. XRD analysis demonstrates that traces of Pr³⁺ can enlarge the lattice parameter of Li₄Ti₅O₁₂ from 8.3403 to 8.3765 Å without changing the spinel structure. The increase of lattice parameter is beneficial to the intercalation and de-intercalation of lithium-ion. XPS results identify the existence form of Ti is mainly Ti⁴⁺ and Ti³⁺ in minor quantity in Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0.05) samples due to the small amount of Pr³⁺. The transition from Ti⁴⁺ to Ti³⁺ is conducive to the electronic conductivity of Li₄Ti₅O₁₂. FESEM images show that all the nanofibers are well crystallized with a diameter of about 200 nm and distributed uniformly. The results of electrochemical measurement reveal that the 1D Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0.05) nanofibers display enhanced high-rate capability and cycling stability compared with that of undoped nanofibers. The high-rate discharge capacity of the Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0.05) samples is excellent (101.6 mAh g^?1 at 50 °C), which is about 58.48 % of the discharge capacity at 0.2 °C and 4.3 times than that of the bare Li₄Ti₅O₁₂ (23.5 mA g^?1). Even at 10 °C (1750 mA g^?1), the specific discharge capacity is still 112.8 mAh g^?1 after 1000 cycles (87.9 % of the initial discharge capacity). The results of cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) illustrate that the Pr-doped Li₄Ti₅O₁₂ electrodes possess better dynamic performance than the pure Li₄Ti₅O₁₂, further confirming the excellent electrochemical properties above.     

Hierarchical LiMn<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>PO<Subscript>4</Subscript>/C nanorods with excellent electrochemical performance synthesized by rheological phase method as cathode for lithium ion battery

The hierarchical LiMn_0.5Fe_0.5PO₄/C (LMFP) nanorods were first successfully synthesized by rheological phase method using polyethylene glycol 4000 (PEG 4000) as a template reagent. The physical and electrochemical properties of the LiMn_0.5Fe_0.5PO₄/C were characterized by TG-DTG, XRD, FTIR, SEM, TEM, EIS and galvanostatic charge-discharge measurements. The results reveal that the PEG-LMFP/C synthesized with the assistance of PEG 4000 shows unique bundle-type shape assembled of nanorods, while the LMFP/C synthesized without PEG 4000 presents a platelet-like shape with some agglomeration. Besides, a uniformly carbon layer coating on the surface of the PEG-LMFP/C can be seen from TEM images. The PEG-LMFP/C exhibits high specific capacity and superior rate performance with discharge capacities of 162, 133, 108, 95, and 78 mAh?·?g^?1 at 0.1, 1, 5, 10, and 20 C rates, respectively. It is demonstrated that the synthesis of LMFP/C with PEG 4000 can significantly decrease the characteristic sizes of the crystals, resulting in improved electrochemical performance.     

Synthesis of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>-reduced graphene oxide composite and its application for hybrid supercapacitors

We describe in this paper the synthesis and the characterization of Li₄Ti₅O₁₂-reduced graphene oxide (LTO-RGO) composite and demonstrate their use as hybrid supercapacitor, which is consist of an LTO negative electrode and activate carbon (AC) positive electrode. The LTO-RGO composites were synthesized using a simple, one-step process, in which lithium sources and titanium sources were dissolved in a graphene oxide (GO) suspension and then thermal treated in N₂. The lithium-ion battery with LTO-RGO composite anode electrode revealed higher discharge capacity (167 mAh g^?1 at 0.2 C) and better capacity retention (67%) than the one with pure LTO. Meanwhile, compared with the AC//LTO supercapacitor, the AC//LTO-RGO hybrid supercapacitor exhibits higher energy density and power density. Results show that the LTO-RGO composite is a very promising anode material for hybrid supercapacitor.     

Titanium-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> with a synergistic effect of surface modifying,bulk doping,and size reducing

In this work, a one-step solid-phase sintering process via TiO₂ and Li₂CO₃ under an argon atmosphere, with ultra-fine titanium powder as the modifying agent, was used to prepare a nano-sized Li₄Ti₅O₁₂/Ti composite (denoted as LTO–Ti) at 800 °C. The introduction of ultra-fine metal titanium powder played an important role. First, X-ray photoelectron spectroscopy demonstrates that Ti⁴⁺ was partially changed into Ti³⁺, through the reduction of the ultra-fine metal titanium powder. Second, X-ray diffraction revealed that the ultra-fine metal titanium powder did not react with the bulk structure of Li₄Ti₅O₁₂, while some pure titanium peaks could be seen. Additionally, the size of LTO–Ti particles could be significantly reduced from micro-scale to nano-scale. The structure and morphology of LTO–Ti were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical tests showed a charge/discharge current of 0.5, 1, 5, and 10 C; the discharge capacity of the LTO–Ti electrode was 170, 161, 140, and 111 mAh g^?1. It is believed that the designed LTO–Ti composite makes full use of both components, thus offering a large contact area between the electrolyte and electrode, high electrical conductivity, and lithium-ion diffusion coefficient during electrochemical processes. Furthermore, ultra-fine titanium powder, as the modifying agent, is amenable to large-scale production.     

Synthesis of spinel LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> as advanced cathode via a modified oxalate co-precipitation method

Spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) cathode materials for lithium ion batteries have been synthesized via a modified oxalate co-precipitation method. By virtue of the co-precipitation of Li⁺ with transition metal ions, the target materials can be obtained through one-pot reaction without subsequent mixing with lithium salts. What’s more, a uniform distribution between the lithium and transition metal ions at molecular level could be realized, which is beneficial for final electrochemical performances. The physical and electrochemical properties of the material are characterized by XRD, TGA, EDS, FT-IR, SEM, CV, EIS, and charge/discharge tests. The results prove that the as-prepared material owns a cubic spinel structure with a space group of Fd-3m, high crystallinity, uniform particle size, and excellent electrochemical performances. A higher initial capacity and superior rate performance are delivered compared with that of material by conventional co-precipitation method. High capacities of 131.7 and 104.0 mAh g^?1 could be displayed at 0.5 and 10 C, respectively. Excellent cycle stability is also demonstrated with more than 98.5 % capacity retention after 100 cycles at 1 C.     

Improved electrochemical properties of YF<Subscript>3</Subscript>-coated Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> as cathode for Li-ion batteries

Yttrium fluoride YF₃ layer with different coating contents is successfully covered on the surface of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ via a common wet chemical approach. The XRD, SEM, TEM, and charge-discharge tests are applied to investigate the influence of YF₃ layer on the micro-structural, morphology, and electrochemical properties of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂. And the electrochemical test results demonstrate that the YF₃-coated LMNCO samples exhibit the improved electrochemical properties. The 2wt.%YF₃-coated LMNCO delivers a discharge capacity of 116.6 mAh g^?1 at 5 C rate, much larger than that (95.6 mAh g^?1) of the pristine one. Besides, the electrochemical impedance spectroscopy (EIS) and cyclic voltammetric results indicate that the YF₃ coating layer can promote the optimization formation of SEI film and reversibility of the electrochemical redox.     

Electrochemical comparison of LiFe<Subscript>0.4</Subscript>Mn<Subscript>0.595</Subscript>Cr<Subscript>0.005</Subscript>PO<Subscript>4</Subscript>/C and LiMnPO<Subscript>4</Subscript>/C cathode materials

A comparison of electrochemical performance between LiFe_0.4Mn_0.595Cr_0.005PO₄/C and LiMnPO₄/C cathode materials was conducted in this paper. The cathode samples were synthesized by a nano-milling-assisted solid-state process using caramel as carbon sources. The prepared samples were investigated by XRD, SEM, TEM, energy-dispersive X-ray spectroscopy (EDAX), powder conductivity test (PCT), carbon-sulfur analysis, electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge cycling. The results showed that LiFe_0.4Mn_0.595Cr_0.005PO₄/C exhibited high specific capacity and high energy density. The initial discharge capacity of LiFe_0.4Mn_0.595Cr_0.005PO₄/C was 163.6 mAh g^?1 at 0.1C (1C = 160 mA g^?1), compared to 112.3 mAh g^?1 for LiMnPO₄/C. Moreover, the Fe/Cr-substituted sample showed good cycle stability and rate performance. The capacity retention of LiFe_0.4Mn_0.595Cr_0.005PO₄/C was 98.84 % over 100 charge-discharge cycles, while it was only 86.64 % for the pristine LiMnPO₄/C. These results indicated that Fe/Cr substitution enhanced the electronic conductivity for the prepared sample and facilitated the Li⁺ diffusion in the structure. Furthermore, LiFe_0.4Mn_0.595Cr_0.005PO₄/C composite presented high energy density (606 Wh kg^?1) and high power density (574 W kg^?1), thus suggested great potential application in lithium ion batteries (LIBs).     

LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> hollow nano-micro hierarchical microspheres as advanced cathode for lithium ion batteries

The high-voltage spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode material for next-generation lithium ion batteries. In this study, hollow LNMO microspheres have been synthesized via co-precipitation method accompanied with high-temperature calcinations. The physical and electrochemical properties of the materials are characterized by x-ray diffraction (XRD), TGA, RAMAN, CV, scanning electron microscope (SEM), transmission electon microscopy (TEM), electrochemical impendence spectroscopy (EIS), and charge-discharge tests. The results prove that the microspheres combine hollow structures inward and own a cubic spinel structure with space group of Fd-3m, high crystallinity, and excellent electrochemical performances. With the short Li⁺ diffusion length and hollow structure, the hierarchical LNMO microspheres exhibit 138.2 and 108.5 mAh g^?1 at 0.5 and 10 C, respectively. Excellent cycle stability is also demonstrated with more than 98.8 and 88.2 % capacity retention after 100 cycles at 1 and 10 C, respectively.     

Urea-assisted solvothermal synthesis of monodisperse multiporous hierarchical micro/nanostructured ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres and their lithium storage properties

High-quality monodisperse multiporous hierarchical micro/nanostructured ZnCo₂O₄ microspheres have been fabricated by calcinating the Zn_1/3Co_2/3CO₃ precursor prepared by urea-assisted solvothermal method. The as-prepared products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller (BET) measurement to study the crystal phase and morphology. When tested as anode material for lithium ion batteries, the multiporous ZnCo₂O₄ microspheres exhibit an initial discharge capacity of 1,369 mAh g^?1 (3,244.5 F cm^?3) and retain stable capacity of 800 mAh g^?1 (1,896 F cm^?3) after 30 cycles. It should be noted that the good electrochemical performances can be attributed to the porous structure composed of interconnected nanoscale particles, which can promote electrolyte diffusion and reduce volume change during discharge/charge processes. More importantly, this ZnCo₂O₄ 3D hierarchical structures provide a large number of active surface position for Li⁺ diffusion, which may contribute to the improved electrochemical performance towards lithium storage.     

The facile in situ preparation and characterization of C/FeOF/FeF<Subscript>3</Subscript> nanocomposites as LIB cathode materials

C/FeOF/FeF₃ nanocomposite was synthesized by a facile in situ partial oxidation method. High-resolution transmission electron microscopy (HR-TEM) showed a special texture comprised of interpenetrating nanodomains of FeOF and FeF₃. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that the introduction of nanodomain FeOF enhanced both the electronic and ionic conductivity of the composite material. Therefore, the improvement of electron and lithium-ion dynamics resulted in the significant enhancement of the electrochemical performances of the material at ambient temperature. At a current density of 20 mA g^?1 within potential range 1.5–4.5 V, the specific capacities of the first ten circles were maintained at about 400 mAh g^?1 _. This material also exhibited excellent cycling capacity retention capability especially for high C rates. When the current density further increased to 100 and 200 mA g^?1, a steady capacity of 80 and 60 mAh g^?1 was observed, respectively. Furthermore, nearly no capacity loss was observed for the followed cycles. The discharge platforms based on intercalation and conversion reaction were also heightened by about 0.4 V, which increased the contribution of high voltage capacities. Compared to C/FeF₃, C/FeOF/FeF₃ is showing more of capacitive behavior, which also contributes to the high specific capacity delivered and is believed to be closely related to the enlarged nanodomain interfaces between two electrochemical active materials. An expansion-cracking-oxidation mechanism was proposed to explain the formation of this interpenetrating nanodomains of FeOF and FeF₃.