Among the Li-rich layered oxides Li2MnO3 has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine Li2MnO3 generally has to be electrochemically activated in the first charge–discharge cycle which causes very low Coulombic efficiency and thus deteriorates its electrochemical properties. In this work, we show that low-temperature reduction can produce a large amount of structural defects such as oxygen vacancies, stacking faults, and orthorhombic LiMnO2 in Li2MnO3. The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine Li2MnO3 changes into a Li2MnO3–LiMnO2 (0.71/0.29) composite, and the monoclinic Li2MnO3 changes from Li2.04Mn0.96O3 in the pristine Li2MnO3 (P–Li2MnO3) to Li2.1Mn0.9O2.79 in the reduced Li2MnO3 (R-Li2MnO3), indicating the production of a large amount of oxygen vacancies in the R-Li2MnO3. High-resolution transmission electron microscope images show that a high density of stacking faults is also introduced by the low-temperature reduction. When measured as a cathode material for Li-ion batteries, R-Li2MnO3 shows much better electrochemical properties than P-Li2MnO3. For example, when charged–discharged galvanostatically at 20 mA·g–1 in a voltage window of 2.0–4.8 V, R-Li2MnO3 has Coulombic efficiency of 77.1% in the first charge–discharge cycle, with discharge capacities of 213.8 and 200.5 mA·h·g–1 in the 20th and 30th cycles, respectively. In contrast, under the same charge–discharge conditions, P-Li2MnO3 has Coulombic efficiency of 33.6% in the first charge–discharge cycle, with small discharge capacities of 80.5 and 69.8 mA·h·g–1 in the 20th and 30th cycles, respectively. These materials characterizations, and electrochemical measurements show that low-temperature reduction is one of the effective ways to enhance the performances of Li2MnO3 as a cathode material for Li-ion batteries.Keywords: cathode materials; Li-rich manganese-based layered oxides; Li2MnO3; lithium-ion batteries; nanobelts;

Spinel phase LiMn2O4 was successfully embedded into monoclinic phase layeredstructured Li2MnO3 nanorods, and these spinel-layered integrate structured nanorods showed both high capacities and superior high-rate capabilities as cathode material for lithium-ion batteries (LIBs). Pristine Li2MnO3 nanorods were synthesized by a simple rheological phase method using α-MnO2 nanowires as precursors. The spinel-layered integrate structured nanorods were fabricated by a facile partial reduction reaction using stearic acid as the reductant. Both structural characterizations and electrochemical properties of the integrate structured nanorods verified that LiMn2O4 nanodomains were embedded inside the pristine Li2MnO3 nanorods. When used as cathode materials for LIBs, the spinel-layered integrate structured Li2MnO3 nanorods (SL-Li2MnO3) showed much better performances than the pristine layered-structured Li2MnO3 nanorods (L-Li2MnO3). When charge–discharged at 20 mA·g−1 in a voltage window of 2.0–4.8 V, the SL-Li2MnO3 showed discharge capacities of 272.3 and 228.4 mAh·g−1 in the first and the 60th cycles, respectively, with capacity retention of 83.8%. The SL-Li2MnO3 also showed superior high-rate performances. When cycled at rates of 1 C, 2 C, 5 C, and 10 C (1 C = 200 mA·g−1) for hundreds of cycles, the discharge capacities of the SL-Li2MnO3 reached 218.9, 200.5, 147.1, and 123.9 mAh·g−1, respectively. The superior performances of the SL-Li2MnO3 are ascribed to the spinel-layered integrated structures. With large capacities and superior high-rate performances, these spinel-layered integrate structured materials are good candidates for cathodes of next-generation high-power LIBs.

•A Li2MnSiO4/carbon/graphene composite was synthesized by a facile one-step method.•Li2MnSiO4/C/G composite showed superior high-rate performances as cathode for LIBs.•Discharge capacities of 271 mAh g−1 can be reached at the charge–discharge rate of 0.1 C.•Discharge capacities of 109 mAh g−1 can be reached at the charge–discharge rate of 10 C.•Charge-transfer resistance and Li-ions diffusion coefficient were calculated.In this paper, a Li2MnSiO4/carbon/graphene (LMS/C/G) composite is synthesized by a facile one-step synthesis method and shows superior high-rate performances as the cathode materials for lithium ion batteries (LIBs). In the LMS/C/G composite, carbon coated Li2MnSiO4 particles, with sizes of 20–30 nm, are uniformly anchored on graphene nanosheets. When assembled as the cathodes of LIBs and charge–discharged at the high rates of 1 C, 2 C, 5 C and 10 C (1 C = 166 mA g−1), the specific discharge capacities of the LMS/C/G composite can reach 210, 181, 143, and 109 mAh g−1, respectively. These electrochemical performances are much better than the performances of the Li2MnSiO4 composites that simply coated with carbon (LMS/C) or merely wrapped by graphene sheets (LMS/G). Electrochemical impedance spectroscopy (EIS) analysis shows that, compared with composites LMS/G and LMS/C, composite LMS/C/G has smaller charge-transfer resistance through the solid-electrolyte interfaces and faster lithium ions diffusion coefficient in the cathode materials. These much improved electronic and ionic conductivities should account for the superior high-rate performances of the LMS/C/G composite.

The effects of vanadium pentoxide on the electrochemical properties of Li2MnSiO4 as a cathode material for lithium-ion batteries were tested by synthesizing a V2O5 nanowire-modified in situ carbon coated Li2MnSiO4 composite (LMS/C/V2O5) and comparing its performances with that of a Li2MnSiO4 composite without V2O5. In LMS/C/V2O5, the V2O5 nanowires, with diameters of around 10–20 nm and lengths up to tens of micrometers, entangled together and formed a 3D conductive network; the Li2MnSiO4 nanoparticles, with sizes around 30 nm, distributed uniformly in the network frame and tended to adhere to the V2O5 nanowires. In this structure, the LMS/C/V2O5 composite showed a superior performance as a cathode of lithium-ion batteries even with very low carbon content (3.4 wt%). Ex situ X-ray diffraction patterns, electrochemical impedance spectroscopies of the electrodes and the concentration of Mn ions in the electrolyte during the charge–discharge processes explained the effects of the V2O5 nanowires as an additive in the Li2MnSiO4 cathode material. The benefits of the nanowires include maintaining the crystal structure of Li2MnSiO4 during the charge–discharge cyclings, reducing the charge-transfer resistances at the solid–electrolyte interfaces, increasing the lithium ions diffusion coefficient in the cathode and alleviating the dissolution of manganese into the electrolyte of the batteries.

Three-dimensional macroporous graphene-based Li2FeSiO4 composites (3D-G/Li2FeSiO4/C) were synthesized and tested as the cathode materials for lithium-ion batteries. To demonstrate the superiority of this structure, the composite’s performances were compared with the performances of two-dimensional graphene nanosheets-based Li2FeSiO4 composites (2D-G/Li2FeSiO4/C) and Li2FeSiO4 composites without graphene (Li2FeSiO4/C). Due to the existence of electronic conductive graphene, both 3D-G/Li2FeSiO4/C and 2D-G/Li2FeSiO4/C showed much improved electrochemical performances than the Li2FeSiO4/C composite. When compared with the 2D-G/Li2FeSiO4/C composite, 3D-G/Li2FeSiO4/C exhibited even better performances, with the discharge capacities reaching 313, 255, 215, 180, 150, and 108 mAh g–1 at the charge–discharge rates of 0.1 C, 1 C, 2 C, 5 C, 10 C and 20 C (1 C = 166 mA g–1), respectively. The 3D-G/Li2FeSiO4/C composite also showed excellent cyclability, with capacity retention exceeding 90% after cycling for 100 times at the charge–discharge rate of 1 C. The superior electrochemical properties of the 3D-G/Li2FeSiO4/C composite are attributed to its unique structure. Compared with 2D graphene nanosheets, which tend to assemble into macroscopic paper-like structures, 3D macroporous graphene can not only provide higher accessible surface area for the Li2FeSiO4 nanoparticles in the composite but also allow the electrolyte ions to diffuse inside and through the 3D network of the cathode material. Specially, the fabrication method described in this study is general and thus should be readily applicable to the other energy storage and conversion applications in which efficient ionic and electronic transport is critical.Keywords: cathode materials; graphene; Li2FeSiO4/C; lithium-ion batteries; macroporous

•A novel graphene-containing Li2FeSiO4 composite (Li2FeSiO4/C/G) has been synthesized.•When used as cathode materials for Li-ion batteries, the Li2FeSiO4/C/G composite shows superior large capacities and long-time cyclabilities.•Specific discharge capacities of 310 mAh g−1 can be reached at the charging-discharging rate of 0.1 C.•At high rates of 30 C and 50 C, the composite shows ∼110 and ∼50 mAh g−1 discharge capacities after 1000 cyclings.A novel graphene-containing Li2FeSiO4 composite (Li2FeSiO4/C/G) has been synthesized successfully which shows superior performance when used as the cathode material for lithium ion batteries. The Li2FeSiO4/C precursor was synthesized via a modified sol-gel method and mixed with graphene oxide nanosheets which were then reduced by annealing to obtain electron conductive graphene. The structure characterizations by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) show that phase-pure Li2FeSiO4/C nanoparticles are mixed homogeneously with graphene nanosheets. When used as the cathode materials for rechargeable lithium ion batteries, the composite Li2FeSiO4/C/G shows superior large capacities and long-time cyclabilities. Specific discharge capacities of 310 mAh g−1, corresponding to 1.86 Li+ ions exchange per Li2FeSiO4 molecule, can be reached at the charging/discharging rate of 0.1 C (1 C = 166 mA g−1). At the high rate of 30 C and 50 C, the composite still shows ∼110 and ∼50 mAh g−1 discharge capacities after 1000 charging-discharging cyclings. These superior–the best up to now–performances of the composite are believed to be the cooperative result of the 3D conducting network, formed by the flexible and planar graphene nanosheets, and the nanoscale sizes of the carbon-coated Li2FeSiO4 particles.

Nanoworm-like Li2FeSiO4–C composites are synthesized using triblock copolymer Pluronic P123 (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), EO20PO70EO20) as the structure directing agent (SDA) and under the effects of ethanol. As a polar nonaqueous cosolvent, ethanol has effects on the self-organization behavior of Pluronic P123 in water, which determines the final morphologies of the Li2FeSiO4–C composites synthesized. Li2FeSiO4–C composite nanoparticles are obtained if no ethanol is added into the system during the synthesis process. When tested as lithium-ion battery cathodes, the Li2FeSiO4–C nanoworms show superior electrochemical performances. At the rate of 1 C (1 C = 166 mA g–1) the discharge capacity of the Li2FeSiO4–C nanoworms can reach 166 mAh g–1 in the voltage window of 1.5–4.8 V at room temperature. At the rates of 5, 10, and 20 C, the discharge capacities of the Li2FeSiO4–C nanoworms can stabilize at 120, 110, and 90 mAh g–1, respectively, and do not show obvious declines after hundreds of cycles. This performance of the Li2FeSiO4–C nanoworms at high rates is better than that of the Li2FeSiO4–C nanoparticles synthesized and many other Li2FeSiO4/C composites reported in the literature. The excellent electrochemical performances of the Li2FeSiO4–C nanoworms are believed to be related to the small sizes of the Li2FeSiO4 nanocrystals inside the nanoworms and the carbon that coats and embeds the nanocrystals.Keywords: cathode materials; Li2FeSiO4−C; lithium ion batteries; nanoworms;

Efforts were made to synthesize LiFePO4/C composites showing both high rate capability and high tap density. First, monoclinic phase FePO4·2H2O with micro-nano hierarchical structures are synthesized using a hydrothermal method, which are then lithiated to LiFePO4/C also with hierarchical structures by a simple rheological phase method. The primary structures of FePO4·2H2O are nanoplates with ∼30 nm thickness, and the secondary structures of the materials are intertwisted micro-scale rings. The LiFePO4/C materials lithiated from these specially structured precursors also have hierarchical structures, showing discharge capacities of more than 120, 110, and 90 mAh g−1 at rates of 5 C, 10 C and 20 C, respectively, and high tap density of 1.4 g cm−3 as cathode materials for lithium ion batteries. Since tap density is an important factor that needs to be considered in fabricating real batteries in industry, these hierarchical structured LiFePO4/C moves closer to real and large-scale applications.

LiFePO4/C microspheres composed of many densely compact nanoplates were synthesized by a simple rheological phase method using nanoplate assembled quasi-microspheres of FePO4·2H2O as raw materials. The quasi-sphere FePO4·2H2O precursors were synthesized via a sodium dodecylsulfate assisted hydrothermal process. Both the LiFePO4/C composite and the FePO4·2H2O precursors were characterized by XRD, TG, SEM, TEM, and Raman spectroscopy. The FePO4·2H2O quasi-spheres had a size distribution of about 1 μm and were composed of nanoplates with a 30 nm thickness. The LiFePO4/C microspheres were also composed of the same sized nanoplates with an ∼2 nm thick amorphous carbon layer coating at the surface. The as-synthesized LiFePO4/C composite showed excellent high-rate capability, with discharge capacities reaching 116, 96 and 75 mAh g−1 at 10 C, 20 C and 30 C current rates, respectively. Furthermore, the LiFePO4/C material composed of microspheres had a high tap density (1.4 g cm−3). Therefore, this LiFePO4/C material can be the cathode material for large-scale applications such as electric vehicles and plug-in hybrid electric vehicles.

Monoclinic phase FePO4·2H2O nanoplates are synthesized very easily in a waterbath and are lithiated to LiFePO4/C nanoparticles by a simple rheological phase method. The thickness of the nanoplates can be tuned simply by changing the concentrations of the reactants. The LiFePO4/C nanoparticles lithiated from the thin FePO4·2H2O nanoplates, with the sizes about 50 nm and the carbon coating layer at the surface 1–2 nm, show excellent high-rate performance and long-term cyclability as the cathode for lithium ion batteries, delivering discharge capacities of more than 150, 120, 110, 100, and 75 mAh g−1 at rates of 5 C, 10 C, 15 C, 20 C and 30 C, respectively.Research highlights► Monoclinic phase FePO4·2H2O nanoplates are synthesized in waterbath. ► The thickness of the FePO4·2H2O nanoplates can be easily tuned. ► FePO4·2H2O nanoplates are lithiated to LiFePO4/C nanoparticles. ► The LiFePO4/C nanoparticles have sizes ∼50 nm, with carbon coating layer ∼2 nm. ► The nanoparticles show excellent high-rate performance and long-term cyclability.

Hematite (α-Fe2O3) nanoflakes and nanocubes were synthesized by liquid–solid-solution method and their properties as anode electrode materials for rechargeable Li+-ion batteries were measured. When changing the water to ethanol volume ratio in the synthesis system, the nanocrystals can be changed from α-Fe2O3 to α-FeOOH, with shapes being tuned from nanoflakes to nanocubes, non-uniform particles and nanowires. When assembled as the anode electrode materials in rechargeable Li+-ion batteries, the hematite nanoflakes showed one more plateau in the first discharge progress of the voltage–composition curves than hematite nanocrystals with other shapes in the literature. X-ray diffraction, high-resolution transmission electron microscope and electrochemical data showed that this extra plateau came from the formation of Li2Fe3O4 nanoclusters and amorphous Li2O. This experiment showed that like sizes, shapes of nanocrystals may also affect the detailed electrochemical progress.

Although various transition metal oxides have been reported to act as low potential Li insertion hosts, the oxyhydroxides have remained unexplored to date. We show here that the hydroxide ions present in transition metal oxyhydroxides do not interfere with the lithium uptake and extraction, permitting very good reversibility of the reduction/oxidation reactions. Goethite (α-FeOOH) nanocrystals can uptake and extract large amount of Li via the conversion reaction mechanism, providing a reversible capacity of 500 mA h g−1 at an average potential of 0.85 V vs. Li/Li+. The mechanism was examined using a combination of X-ray diffraction, electron microscopy, and the corresponding selected area electron diffractions (SAEDs). The α-FeOOH is reduced into nanoparticles of metallic Fe0 embedded in an amorphous matrix of Li2O and LiOH in the first discharge; the subsequent cyclings are redox reactions between metallic Fe0 and Fe2O3 clusters.

LiFePO4/C microspheres composed of many densely compact nanoplates were synthesized by a simple rheological phase method using nanoplate assembled quasi-microspheres of FePO4·2H2O as raw materials. The quasi-sphere FePO4·2H2O precursors were synthesized via a sodium dodecylsulfate assisted hydrothermal process. Both the LiFePO4/C composite and the FePO4·2H2O precursors were characterized by XRD, TG, SEM, TEM, and Raman spectroscopy. The FePO4·2H2O quasi-spheres had a size distribution of about 1 μm and were composed of nanoplates with a 30 nm thickness. The LiFePO4/C microspheres were also composed of the same sized nanoplates with an ∼2 nm thick amorphous carbon layer coating at the surface. The as-synthesized LiFePO4/C composite showed excellent high-rate capability, with discharge capacities reaching 116, 96 and 75 mAh g−1 at 10 C, 20 C and 30 C current rates, respectively. Furthermore, the LiFePO4/C material composed of microspheres had a high tap density (1.4 g cm−3). Therefore, this LiFePO4/C material can be the cathode material for large-scale applications such as electric vehicles and plug-in hybrid electric vehicles.