LiFePO<Subscript>4</Subscript> composites decorated with nitrogen-doped carbon as superior cathode materials for lithium-ion batteries

The development of methods to synthesize electrode materials can improve the performance of lithium ion storage. In this study, a facile and low-cost approach is employed to synthesize LiFePO₄ (LFP/NC) hybrid materials decorated with nitrogen-doped carbon nanomaterials (NC). Melamine was used as nitrogen and carbon source with an NC to LFP ratio of 3.19%. As electrode materials for lithium ion batteries (LIBs), the LFP/NC composites exhibit an optimum performance with a high rate capacity of 144.6 mAh·g^?1 at 1 C after 500 cycles without apparent loss. The outstanding cycling stability may be attributed to the synergetic effects of well-crystallized particles and NC layers.     

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.     

Surfactant-assisted synthesis of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> particles as high-rate and long-life cathode materials for lithium-ion batteries

Herein, we reported the synthesis of uniform LiMn₂O₄ submicroparticles by surfactant-assisted preparation of spherical MnCO₃ precursor followed by solid-state reaction. Polyethylene glycol (Mw = 1000) was used as surfactant to control the morphology and size of the MnCO₃ precursor as well as the MnO₂ intermediate and LiMn₂O₄ product. The influence of particle size, homogeneity, and crystallinity on the electrochemical performance of LiMn₂O₄ was intensively investigated. The test results indicate that the LiMn₂O₄ sample using polyethylene glycol with weight as 10% of reactants shows the best rate capability and long-term cyclability. Due to the homogeneous particles with the average size of ca. 250 nm and high crystallinity, the discharge capacities are as high as 125, 118, 114, and 100 mAh g^?1 at 1, 10, 20, and 50 C rates, respectively, along with high capacity retention of 74% after 1000 cycles at 20 C.     

Improved of cathode performance of LiFePO<Subscript>4</Subscript>/C composite using different carboxylic acids as carbon sources for lithium-ion batteries

Among the several materials under development for use as a cathodes in lithium-ion batteries olivine-type LiFePO₄ is one of the most promising cathode material. However, its poor conductivity and low lithium-ion diffusion limits its practical application. In this study, we report seven different carboxylic acids used to synthesize LiFePO₄/C composite, and influences of carbon sources on electrochemical performance were intensively studied. The structure and electrochemical properties of the LiFePO₄/C were characterized by X-ray diffraction, scanning electron microscopy, electrical conductivity, and galvanostatic charge–discharge measurements. Among the materials studied, the sample E with tartaric acid as carbon source exhibited the best cell performance with a maximum discharge capacity of 160 mAh g⁻¹ at a 0.1 C-rate. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by carbon.     

Preparation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> hollow microsphere/graphene/carbon nanotube flexible film as a binder-free anode material for lithium-ion batteries

A flexible Co₃O₄ hollow microsphere/graphene/carbon nanotube hybrid film is successfully prepared through a facile filtration strategy and a subsequent thermally treated process. The composition, morphology, and structure of the as-prepared film are characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. Based on the morphology characterizations on the hybrid film, the Co₃O₄ hollow microspheres are uniformly and closely attached on three-dimensional (3D) graphene/carbon nanotubes (GR/CNTs) network, which decreases the agglomeration of Co₃O₄ microspheres effectively. In this hybrid film, the 3D GR/CNT network which enhances conductance as well as prevents aggregation is a benefit to help Co₃O₄ to exert its lithium storage capabilities sufficiently. When used as a binder-free anode material for lithium-ion batteries, the hybrid film delivers excellent electrochemical properties involving reversible capacity (863 mAh g^?1 at a current density of 100 mA g^?1) and rate performance (185 mAh g^?1 at a current density of 1600 mA g^?1).     

A novel approach to employ Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript> as anode active material for lithium batteries

In the present paper, we describe utilization of cathode active material as anode active material, for example, Li₂MnSiO₄. The lithium manganese silicate has been successfully synthesized by solid-state reaction method. The X-ray diffraction pattern confirms the orthorhombic structure with Pmn2 ₁ space group. The Li/Li₂MnSiO₄ cell delivered the initial discharge capacity of 420 mA h g⁻¹, which is 110 mA h g⁻¹ higher than graphitic anodes. The electrochemical reversibility and solid electrolyte interface formation of the Li₂MnSiO₄ electrode was emphasized by cyclic voltammetry.     

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.     

Cu-supported carbon networks containing SnO<Subscript>2</Subscript> as three-dimensional anodes for lithium-ion batteries

Cu-supported SnO₂@C composite coatings constructed by interconnected carbon-based porous branches were fabricated by annealing Cu foils with films formed by knife coating DMF solution containing SnCl₂, polyacrylonitrile (PAN), and poly(methyl methacrylate) (PMMA) on their surface in vacuum. The carbon-based porous branches consist of amorphous carbon matrices, SnO₂ nanoparticles with a size of 30–100 nm mainly encapsulated inside, and many micropores with a size of 1–5 nm. The three-dimensional (3D) porous network structures of the SnO₂@C composite were achieved by volatilization of PMMA and pyrolysis of SnCl₂. The SnO₂@C composite coatings demonstrate good cyclic performance with a high reversible capacity of 642 mA h g^?1 after 100 cycles at a current density of 50 mA g^?1 without apparent capacity fading during cycling and excellent rate performance with a capacity of 276 mA h g^?1 at a high current density up to 10 A g^?1.     

Synthesis and electrochemical performance of carbon-coated LiMnBO<Subscript>3</Subscript> as cathode materials for lithium-ion batteries

Carbon-coated LiMnBO₃/C is synthesized by a sol-gel method using polyethylene glycol 6000 (PEG-6000) as carbon source. The influences of different sintering temperatures on the crystal structure, morphology, and electrochemical performance of LiMnBO₃/C composites are investigated. XRD results indicate that the samples consist of the monoclinic phase LiMnBO₃ (m-LiMnBO₃) and the hexagonal phase LiMnBO₃ (h-LiMnBO₃), and the amount of m-LiMnBO₃ is reduced and the h-LiMnBO₃ is increased with the increasing sintering temperature. The particle size of the samples is about 500 nm, and the surface of the particles is coated with a thick amorphous carbon layer. The LiMnBO₃/C synthesized at 750 °C exhibits the initial discharge capacities of 213.4, 170.8, and 109.7 mAh g^?1 at 0.025, 0.05, and 0.5 C rates, respectively, and shows better cycling performance than that of bare LiMnBO₃. The enhanced electrochemical performance might be largely attributed to the uniformly coated carbon layers from decomposition of the PEG-6000.     

Synthesis and electrochemical performance of carbon-coated LiCoBO<Subscript>3</Subscript> as cathode materials for lithium-ion batteries

Carbon-coated LiCoBO₃ (LiCoBO₃/C) is prepared by sol-gel method and polyethylene glycol 6000 (PEG-6000) is chosen as carbon source. The LiCoBO₃/C sample exhibits an initial discharge capacity of 76.7 mAh g^?1 at 0.1 C, and it can deliver a discharge capacity of 65.9 mAh g^?1 after 50 cycles, while the LiCoBO₃ sample only presents a first discharge capacity of 34.3 and 16.8 mAh g^?1 at the 50th cycle, LiCoBO₃/C sample shows better cycling performance than that of LiCoBO₃. The improved electrochemical properties could be mainly ascribed to the conductive carbon network and the reduced particle size of the LiCoBO₃ powders. Electrochemical impedance spectroscopy (EIS) results confirm that carbon coating decreases the charge transfer resistance and improve the electrochemical reaction kinetics.     

Hierarchical Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@C hollow microspheres with high capacity as an anode material for lithium-ion batteries

Three-dimensional hierarchical Co₃O₄@C hollow microspheres (Co₃O₄@C HSs) are successfully fabricated by a facile and scalable method. The Co₃O₄@C HSs are composed of numerous Co₃O₄ nanoparticles uniformly coated by a thin layer of carbon. Due to its stable 3D hierarchical hollow structure and uniform carbon coating, the Co₃O₄@C HSs exhibit excellent electrochemical performance as an anode material for lithium-ion batteries (LIBs). The Co₃O₄@C HSs electrode delivers a high reversible specific capacity, excellent cycling stability (1672 mAh g^?1 after 100 cycles at 0.2 A g^?1 and 842.7 mAh g^?1 after 600 cycles at 1 A g^?1), and prominent rate performance (580.9 mAh g^?1 at 5 A g^?1). The excellent electrochemical performance makes this 3D hierarchical Co₃O₄@C HS a potential candidate for the anode materials of the next-generation LIBs. In addition, this simple synthetic strategy should also be applicable for synthesizing other 3D hierarchical metal oxide/C composites for energy storage and conversion.     

Synthesis,structure, and electrochemistry of Ag-modified LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials for lithium-ion batteries

The composite of silver-modified lithium manganese oxide were prepared using thermal decomposition method of different mole ratio. Structural characterization was carried out by X-ray diffraction (XRD). XRD analysis revealed different patterns as the content of the dopant in the spinel increases. Phase analysis shows that Ag particles were dispersed on the LiMn₂O₄ surface instead of entering the spinel structure. On the other hand, the electrochemical behavior of cathode powder was examined by using two-electrode test cells consisting of a cathode, metallic lithium as anode, and a solid polymer electrolyte of 0.87PEO-0.13LiCF₃SO₃-0.10DBP. According to the electrochemical tests results, the influence of the Ag additive content on the electrochemical properties of Ag/LiMn₂O₄ composites is clearly shown.     

Vertical aligned V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoneedle arrays grown on Ti substrate as binder-free cathode for lithium-ion batteries

V₂O₅ nanoneedle arrays were grown directly on titanium (Ti) substrate by a facile solvothermal route followed with calcination at 350 °C for 2 h. The as-prepared V₂O₅ nanoneedles are about 50 nm in diameter and 800 nm in length. The electrochemical behavior of V₂O₅ nanoarrays as binder-free cathode for lithium-ion batteries (LIBs) was evaluated by cyclic voltammetry and galvanostatic discharge/charge tests. Compared with V₂O₅ powder electrode, V₂O₅ nanoneedle arrays electrode exhibited improved electrochemical performance in terms of high discharge capacity of 262.5 mA h g^?1 between 2.0 and 4.0 V at 0.2 C, and high capacity retention up to 77.1% after 100 cycles. Under a high current rate of 2 C, a discharge capacity of about 175.6 mA h g^?1 can be maintained. The enhanced performance are mainly due to the intimate contact between V₂O₅ nanoneedle active material and current collector, which enable shortened electron transfer pathway and improved charge transfer kinetics, demonstrating their potential applications in high rate electrochemical storage devices.     

Nitrogen-doped carbon nanofiber decorated LiFePO<Subscript>4</Subscript> composites with superior performance for lithium-ion batteries

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.     

Synthesis and electrochemical performance of LiFePO<Subscript>4</Subscript>/C cathode materials from Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> for high-power lithium-ion batteries

Carbon-coated olivine-structured LiFePO₄/C composites are synthesized via an efficient and low-cost carbothermal reduction method using Fe₂O₃ as iron source at a relative low temperature (600 °C). The effects of two kinds of carbon sources, inorganic (acetylene black) and organic (sucrose), on the structures, morphologies, and lithium storage properties of LiFePO₄/C are evaluated in details. The particle size and distribution of the carbon-coated LiFePO₄ from sucrose (LiFePO₄/SUC) are more uniform than that obtained from acetylene black (LiFePO₄/AB). Moreover, the LiFePO₄/SUC nanocomposite shows superior electrochemical properties such as high discharge capacity of 156 mAh g^?1 at 0.1 C, excellent cyclic stability, and rate capability (78 mAh g^?1 at 20 C), as compared to LiFePO₄/AB. Cyclic voltammetric test discloses that the Li-ion diffusion, the reversibility of lithium extraction/insertion, and electrical conductivity are significantly improved in LiFePO₄/SUC composite. It is believed that olivine-structured LiFePO₄ decorated with carbon from organic carbon source (sucrose) using Fe₂O₃ is a promising cathode for high-power lithium-ion batteries.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> quantum dots on 3D-framed graphene aerogel as an advanced anode material in lithium-ion batteries

Three-dimensional fabricated Fe₃O₄ quantum dots/graphene aerogel materials (Fe₃O₄ QDs/GA) were obtained from a facile hydrothermal strategy, followed by a subsequently heat treatment process. The Fe₃O₄ QDs (2–5 nm) are anchored tightly and dispersed uniformly on the surface of three-dimensional GA. The as-prepared anode materials exhibit a high reversible capacity of 1078 mAh g^?1 at a current density of 100 mA g^?1 after 70 cycles in lithium-ion batteries (LIBs) system. Moreover, the rate capacity still remains 536 mAh g^?1 at 1000 mA g^?1. The enhanced electrochemical performance is attributed to that the GA not only acts as a three-dimensional electronic conductive matrix for the fast transportation of Li⁺ and electrons, but also provides with double protection against the aggregation and pulverization of Fe₃O₄ QDs during cycling. Apparently, the synergistic effects of the three-dimensional GA and the quantum dots are fully utilized. Therefore, the Fe₃O₄ QDs/GA composites are promising materials as advanced anode materials for LIBs.     

Investigation on LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material based on the precursor of nickel-manganese compound for lithium-ion battery

The high-voltage spinel LiNi_0.5Mn_1.5O₄ (LNMO) with submicron particle size (LNMO-850₅P700₁₀) has been synthesized based on nickel-manganese compound, which is obtained from pre-sintering the nickel-manganese hydroxide precipitation at 850 °C. The LNMO materials based on nickel-manganese hydroxide (LNMO-700₁₀, LNMO-850₅700₁₀, and LNMO-850₁₀700₁₀) have also been synthesized for comparison to study the pre-sintering impact on the properties of LiNi_0.5Mn_1.5O₄ material. The morphologies and structures of the obtained samples have been analyzed by X-ray powder diffraction and scanning electron microscopy. The nickel-manganese compound has a spinel structure with high crystallinity, making it a good precursor to form high-performance LNMO with lower content of Mn³⁺ and impurity. The obtained LNMO-850₅P700₁₀ delivers discharge capacities of 125.4 mA h g^?1 at 0.2 C, and the capacity retention of 15 C reaches 73.8 % of the capacity retention of 0.2? C. Furthermore, it shows a superior cyclability with the capacity retention of 96.4 % after 150 cycles at 5 ?C. Compared with the synthesis method without pre-sintering, the synthesis method with pre-sintering can save energy while reaching the same discharge specific capacity.     

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.     

Hydrothermal synthesis and electrochemical performance of Mn-doped V<Subscript>6</Subscript>O<Subscript>13</Subscript> as cathode material for lithium-ion battery

Mn_xV_6?xO₁₃ (x?=?0.01, 0.02, 0.03, 0.04) were successfully synthesized via a simple hydrothermal method followed by heat-treatment. Both crystal domain size, electronic conductivity and the lithium diffusion coefficient of the Mn_xV_6?xO₁₃ samples were influenced by the doping amount of Mn²⁺. When x?=?0.02, the product was nano-sized particles and exhibited the best electrochemical performance. The enhanced electrochemical performance originated from its higher total conductivity and higher lithium diffusion coefficient.     

Influence of carbon additive on the properties of spherical Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> and LiFePO<Subscript>4</Subscript> materials for lithium-ion batteries

Preparing spherical particles with carbon additive is considered as one effective way to improve both high rate performance and tap density of Li₄Ti₅O₁₂ and LiFePO₄ materials. Spherical Li₄Ti₅O₁₂/C and LiFePO₄/C composites are prepared by spray-drying–solid-state reaction method and controlled crystallization–carbothermal reduction method, respectively. The X-ray diffraction characterization, scanning electron microscope, Brunauer–Emmett–Teller, alternating current impedance analyzing, tap density testing, and electrochemical property measurements are investigated. After hybridizing carbon with a proper quantity, the crystal grain size of active materials is remarkably decreased and the electrochemical properties are obviously improved. The Li₄Ti₅O₁₂/C and LiFePO₄/C composites prepared in this work are spherical. The tap density and the specific surface area are as high as 1.71 g cm⁻³ and 8.26 m² g⁻¹ for spherical Li₄Ti₅O₁₂/C, which are 1.35 g cm⁻³ and 18.86 m² g⁻¹ for spherical LiFePO₄/C powders. Between 1.0 and 3.0 V versus Li, the reversible specific capacity of the Li₄Ti₅O₁₂/C is more than 150 mAh g⁻¹ at 1.0-C rate. Between 2.5 and 4.2 V versus Li, the reversible capacity of the LiFePO₄/C is close to 140 mAh g⁻¹ at 1.0-C rate.