Facile synthesis of porous hollow Co3O4 microfibers derived-from metal-organic frameworks as an advanced anode for lithium ion batteries

Co₃O₄, as a promising anode material for the next generation lithium ion batteries to replace graphite, displays high theoretical capacity (890 mAh g⁻¹) and excellent electrochemical properties. However, the drawbacks of its poor cycle performance caused by large volume changes during charge-discharge process and low initial coulombic efficiency due to large irreversible reaction impede its practical application. Herein, we have developed a porous hollow Co₃O₄ microfiber with 500 nm diameter and 60 nm wall thickness synthesized via a facile chemical precipitation method with subsequent thermal decomposition. As an advanced anode for lithium ion batteries, the porous hollow Co₃O₄ microfibers deliver an obviously enhanced electrochemical property in terms of lithium storage capacity (1177.4 mA h g⁻¹ at 100 mA g⁻¹), initial coulombic efficiency (82.9%) and cycle performance (76.6% capacity retention at 200th cycle). This enhancement could be attributed to the well-designed microstructure of porous hollow Co₃O₄ microfibers, which could increase the contact surface area between electrolyte and active materials and accommodate the volume variations via additional void space during cycling.     

Polymer microsphere-assisted synthesis of lithium-rich cathode with improved electrochemical performance

The Li-rich layered cathode material Li_1.165Mn_0.501Ni_0.167Co_0.167O₂ with porous structure has been successfully synthesized through a facile co-precipitation approach followed with a high-temperature calcination treatment, adopting polymer microsphere (PSA) as a template and conductive agent. The PSA-assisted Li_1.165Mn_0.501Ni_0.167Co_0.167O₂ composite exhibits remarkably improved cycling stability and rate capability compared with the bare composite. It delivers a high initial discharge capacity of 267.0 mA h g⁻¹ at 0.1 C (1 C=250 mA g⁻¹) between 2.0 V and 4.65 V. A discharge capacity of 214.9 mA h g ⁻¹ is still obtained after 100 cycles. Furthermore, the diffusion coefficients of Li⁺ investigated by the cyclic voltammetry technique are approximately 10⁻¹⁵–10⁻¹⁴ cm² s⁻¹. Such outstanding performance is mainly ascribed to: on one hand, the carbon residue of PSA after being calcined at high temperature contributes to enhance the electronic conductivity of the electrode and alleviates the volume changes during the Li⁺-insertion/extraction, leading to an improved rate capability; on the other hand, the unique porous structure and small particle size are conductive to increase the exposed electrochemical active surface, shorten Li⁺ diffusion distance and thus enhance the lithium storage capacity.     

Porous nitrogen-doped carbon vegetable-sponges with enhanced lithium storage performance

Porous nitrogen-doped carbon vegetable-sponges (N-DCSs) have been fabricated by chemical treatment of the Cu@C precursors using HNO₃ for the first time. The obtained N-DCSs are porous three-dimensional (3D)-structure and similar to numerous agglomerated fluffy micro-vegetable-sponges. When the precursors are treated by H₂SO₄, carbon vegetable-sponges (CSs) without nitrogen doping are prepared. As anode materials in lithium ion batteries, the as-prepared N-DCSs show improved Li-storage capacity and cycling stability as compared with the pure CSs. They offer 870 mA h g⁻¹ at 0.5 A g⁻¹ after 300 cycles and high reversible capacity with 910 mA h g⁻¹ at 0.2 A g⁻¹ after cycled at different current densities, which are much higher than those of CSs. It is envisaged that the large surface area, unique 3D porous nanostructure and appropriate nitrogen doping are favorable for the superior electrochemical properties of N-DCSs.     

Porous Fe2O3 nanorods anchored on nitrogen-doped graphenes and ultrathin Al2O3 coating by atomic layer deposition for long-lived lithium ion battery anode

Porous iron oxide (Fe₂O₃) nanorods anchored on nitrogen-doped graphene sheets (NGr) were synthesized by a one-step hydrothermal route. After a simple microwave treatment, the iron oxide and graphene composite (NGr-I-M) exhibits excellent electrochemical performances as an anode for lithium ion battery (LIB). A high reversible capacity of 1016 mAh g⁻¹ can be reached at 0.1 A g⁻¹. When NGr-I-M electrode was further coated by 2 ALD cycles of ultrathin Al₂O₃ film, the first cycle Coulombic efficiency (CE), rate performance and cycling stability of the coated electrode can be greatly improved. A stable capacity of 508 mAh g⁻¹ can be achieved at 2 A g⁻¹ for 200 cycles, and an impressive capacity of 249 mAh g⁻¹ at 20 A g⁻¹ can be maintained without capacity fading for 2000 cycles. The excellent electrochemical performance can be attributed to the synergy of porous iron oxide structures, nitrogen-doped graphene framework, and ultrathin Al₂O₃ film coating. These results highlight the importance of a rational design of electrode materials improving ionic and electron transports, and potential of using ALD ultrathin coatings to mitigate capacity fading for ultrafast and long-life battery electrodes.     

Fe3O4 nanoparticles encapsulated in electrospun porous carbon fibers with a compact shell as high-performance anode for lithium ion batteries

Fe₃O₄ nanoparticles encapsulated in porous carbon fibers (Fe₃O₄@PCFs) as anode materials in lithium ion batteries are fabricated by a facile single-nozzle electrospinning technique followed by heat treatment. A mixed solution of polyacrylonitrile (PAN) and polystyrene (PS) containing Fe₃O₄ nanoparticles is utilized to prepare hybrid precursor fibers of Fe₃O₄@PS/PAN. The resulted porous Fe₃O₄/carbon hybrid fibers composed of compact carbon shell and Fe₃O₄-embeded honeycomb-like carbon core are formed due to the thermal decomposition of PS and PAN. The Fe₃O₄@PCF composite demonstrates an initial reversible capacity of 1015 mAh g⁻¹ with 84.4% capacity retention after 80 cycles at a current density of 0.2 A g⁻¹. This electrode also exhibits superior rate capability with current density increasing from 0.1 to 2.0 A g⁻¹, and capacity retention of 91% after 200 cycles at 2.0 A g⁻¹. The exceptionally high performances are attributed to the high electric conductivity and structural stability of the porous carbon fibers with unique structure, which not only buffers the volume change of Fe₃O₄ with the internal space, but also acts as high-efficient transport pathways for ions and electrons. Furthermore, the compact carbon shell can promote the formation of stable solid electrolyte interphase on the fiber surface.     

Effect of graphene nanosheets on electrochemical performance of Li4Ti5O12 in lithium-ion capacitors

In order to improve the electrochemical performance of lithium titanium oxide, Li₄Ti₅O₁₂ (LTO), for the use in the lithium-ion capacitors (LICs) application, LTO/graphene composites were synthesized through a solid state reaction. The composite exhibited an interwoven structure with LTO particles dispersed into graphene nanosheets network rather than an agglomerated state pristine LTO particles. It was found that there is an optimum percentage of graphene additives for the formation of pure LTO phase during the solid state synthesis of LTO/graphene composite. The effect of graphene nanosheets addition on electrochemical performance of LTO was investigated by a systemic characterization of galvanostatic cycling in lithium and lithium-ion cell configuration. The optimized composite exhibited a decreased polarization upon cycling and delivered a specific capacity of 173 mA h g⁻¹ at 0.1 C and a well maintained capacity of 65 mA h g⁻¹ even at 20 C. The energy density of 14 Wh kg⁻¹ at a power density of 2700 W kg⁻¹ was exhibited by a LIC full cell with a balanced mass ratio of anode to cathode along with a superior capacitance retention of 97% after 3000 cycles at a current density of 0.4 A g⁻¹. This boost in reversible capacity, rate capability and cycling performance was attributed to a synergistic effect of graphene nanosheets, which provided a short lithium ion diffusion path as well as facile electron conduction channels.     

Pseudocapacitive Li+ intercalation in ZnO/ZnO@C composites enables high-rate lithium-ion storage and stable cyclability

Metallic oxide ZnO is considered to be a promising alternative anode material for lithium ion battery because of its high theoretical capacities (978 mA h g⁻¹). However, its inherent low electronic conductivity and undesirable large volume change result in inferior electrochemical performances and hinder its practical application. Herein, ZnO/ZnO@C composites are prepared by a simple carbonization process of ZnO/ZnO@ZIFs-8, which are constructed by using ZnO particles as both template and zinc sources for zeolitic imidazolate frameworks-8 (ZIF-8) preparation via a facile solution reaction. When evaluated as anode for lithium ion batteries, the as-prepared composites show an initial capacity of 878 mA h g⁻¹ at current density of 0.1 A g⁻¹ with high capacity retention of 95.6% after 50 cycles, and an initial capacity of 359 mA h g⁻¹ tested at 5.0 A g⁻¹ with a capacity retention of 85.3% after 500 cycles, exhibiting outstanding cycling stability and excellent rate capability. The ameliorated electrochemical performances are mainly attributed to the elevated conductivity and cushioning effects provided by carbon framework derived from ZIF-8, and the enhanced pseudocapacitance behavior originated from the decreased size of ZnO particles and high surface area of ZIFs-derived carbon.     

Facile synthesis of micro-spherical LiMn0.7Fe0.3PO4/C cathodes with advanced cycle life and rate performance for lithium-ion battery

A series of micro-spherical LiMn_0.7Fe_0.3PO₄/C (LMFP) cathode materials are synthesized via co-precipitation method combining spray drying and solid-state reaction. All as-prepared materials are well-characterized to determine their crystal structure, morphology and electrochemical performance. All as-obtained LMFP materials correspond to orthorhombic olivine structure with Pbnm space group and show uniform porous spherical structure with an average particle size of 3 µm and a carbon coating layer of about 3 nm. In particular, the resulting LMFP material prepared at 600 °C exhibits a high discharge capacity of 160 mAh g⁻¹ at 0.1 C. Even at a high rate of 10 C, it can still deliver 133 mAh g⁻¹ and maintain capacity retention of 84.9% after 200 cycles. The excellent electrochemical performance is ascribed to the synergetic effect of porous micro-spherical structure and uniform carbon coating layer.     

Electrospun ZnO–SnO2 composite nanofibers with enhanced electrochemical performance as lithium-ion anodes

ZnO–SnO₂ composite nanofibers with different structures were synthesized by a simple electrospinning approach with subsequent calcination at three different temperatures using polyacrylonitrile as the polymer precursor. The electrochemical performance of the composites for use as anode materials in lithium-ion batteries were investigated. It was found that the ZnO–SnO₂ composite nanofibers calcined at 700 °C showed excellent lithium storage properties in terms of cycling stability and rate capability, compared to those calcined at 800 and 900 °C, respectively. ZnO–SnO₂ composite nanofibers calcined at 700 °C not only delivered high initial discharge and charge capacities of 1450 and 1101 mAh g⁻¹, respectively, with a 75.9% coulombic efficiency, but also maintained a high reversible capacity of 560 mAh g⁻¹ at a current density of 0.1 A g⁻¹ after 100 cycles. Additionally, a high reversible capacity of 591 mAh g⁻¹ was obtained when the current density returned to 0.1 A g⁻¹ after 50 cycling at a high current density of 2 A g⁻¹. The superior electrochemical performance of ZnO–SnO₂ composite nanofibers can be attributed to the unique nanofibrous structure, the smaller particle size and smaller fiber diameter as well as the porous structure and synergistic effect between ZnO and SnO₂.     

Bitter gourd-shaped Ni3V2O8 anode developed by a one-pot metal-organic framework-combustion technique for advanced Li-ion batteries

The present study reports on the one-pot synthesis of Ni₃V₂O₈ (NVO) electrodes by a simple metal organic framework-combustion (MOF-C) technique for anode applications in Li-ion batteries (LIBs). The particle morphology of the prepared NVO is observed to vary as irregular rods, porous bitter gourd and hybrid micro/nano particles depending on the concentration of the framework linker used during synthesis. In specific, the orthorhombic phase and the unique bitter gourd-type secondary structure comprised of agglomerated nanoparticles and porous morphologies is confirmed using powder X-ray diffraction, electron microscopies, X-ray photoelectron spectroscopy and N₂ adsorption–desorption measurements. When tested for lithium batteries as anode, the bitter gourd-type NVO electrode shows an initial discharge capacity of 1362 mA h g⁻¹ and a reversible capacity of 822 mA h g⁻¹ are sustained at a rate of 200 mA g⁻¹ after 100 cycles. Moreover, at 2000 mA g⁻¹, a reversible capacity of 724 mA h g⁻¹ is retained after 500 cycles. Interestingly, the porous bitter gourd-shaped NVO electrode registered significantly high rate performance and reversible specific capacities of 764, 531 and 313 mA h g⁻¹ at high rates of 1, 5 and 10 A g⁻¹, respectively.     

Simple self-assembly of SnS2 entrapped graphene aerogel and its enhanced lithium storage performance

In this work, SnS₂ nanoplates entrapped graphene aerogel has been successfully prepared by simple self-assembly of reduced graphene oxide obtained through mild chemical reduction. Structural and morphological investigations demonstrated that SnS₂ nanoplates are highly dispersed in the three dimensional (3D) porous graphene matrix. When served as anode material for lithium-ion batteries, the electrochemical properties of SnS₂/graphene aerogel (SnS₂/GA) were evaluated by galvanostatic discharge–charge tests, cyclic voltammetry and impedance spectroscopy measurement. Compared with pristine SnS₂, the SnS₂/GA nanocomposite achieved a much higher initial reversible capacity (1186 mAh g⁻¹), superior cyclic stability (1004 mAh g⁻¹ after 60 cycles, corresponding to 84.7% of the initial reversible capacity), as well as better rate capability (650 mAh g⁻¹ at a current density of 1000 mA g⁻¹). This significantly improved lithium storage performance can be attributed to the good integration of SnS₂ nanoplates with 3D porous graphene network, which can not only provide much more active sites and easy access for Li ions intercalation, but also prevent the aggregation of SnS₂ nanoplates and facilitate fast transportation of Li ions and surface electrons during the electrochemical process.     

Three-dimensional hierarchical ZnCo2O4 flower-like microspheres assembled from porous nanosheets: Hydrothermal synthesis and electrochemical properties

In this work, three-dimensional hierarchical ZnCo₂O₄ flower-like microspheres have been synthesized on a large scale via a facile and economical citrate-mediated hydrothermal method followed by an annealing process in air. The as-synthesized ZnCo₂O₄ flower-like microspheres are constructed by numerous interweaving porous nanosheets. According to the experimental results, a formation mechanism involving the assembly of the nanosheets from nanoparticles into flower-like microsphere is proposed. As a virtue of their beneficial structural features, the ZnCo₂O₄ flower-like microspheres exhibit a high lithium storage capacity and excellent cycling stability (1136 mA h g⁻¹ at 100 mA g⁻¹ after 50 cycles). This remarkable electrochemical performance can be ascribed to the hierarchical structure and porous structures in the nanosheets, which effectively increases the contact area between the active materials and the electrolyte, shortening the Li⁺ diffusion pathway and buffering the volume variation during cycling.     

Enhanced electrochemical properties of LiFePO4–silicon composites as positive electrode materials fabricated using a solid-state method

LiFePO₄–silicon composites were fabricated by using a solid-state method for applying positive electrodes in lithium ion batteries. The LiFePO₄–silicon composites were characterized with X-ray diffraction and field emission scanning electron microscopy. Their electrochemical properties were investigated with cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The added silicon not only suppressed the surface corrosion caused by the decreasing H⁺ concentration in the electrolyte, but it also acted as a barrier between the LiFePO₄ particles and LiPF₆ electrolyte, thereby preventing the dissolution of Fe²⁺ in the electrode and enhancing the electrolyte/active material interactions. This resulted in improved lithium-ion transfer kinetics and excellent positive electrode performance, especially at high current densities and different operating temperatures (0, 25, and 50 °C). At 25 °C, the LiFePO₄ composite containing 2 wt% of silicon delivered the best electrochemical performance with a lithium-ion diffusion coefficient of 1.81×10⁻⁹ cm² s⁻¹, a specific discharge capacity of 143 mA h g⁻¹ for the initial cycle, and a capacity retention of 98% after 100 cycles. In contrast, the corresponding values for the pure LiFePO₄ were 1.19×10⁻¹¹ cm² s⁻¹, 115 mA h g⁻¹, and a capacity retention of 76% after 100 cycles, respectively.     

Hollow core–shell ZnMn2O4 microspheres as a high-performance anode material for lithium-ion batteries

The hollow core–shell ZnMn₂O₄ microspheres are successfully prepared by a solvothermal carbon templating method and then a annealing process. The crystal phase and particle morphology of resultant ZnMn₂O₄ microspheres are characterized by XRD and TEM. The electrochemical properties of the ZnMn₂O₄ microspheres as an anode material are investigated for lithium ion batteries. The results show that the ZnMn₂O₄ microspheres exhibit a reversible capacity of 855.8 mA h g⁻¹ at a current density of 200 mA g⁻¹ after 50 cycles. Even at 1000 mA g⁻¹, the reversible capacity of the ZnMn₂O₄ microspheres is still kept at 724.4 mA h g⁻¹ after 60 cycles. The enhanced electrochemical performance suggests the promising potential of the hollow core–shell ZnMn₂O₄ microspheres in lithium-ion batteries.     

A nest-like hierarchical porous V2O5 as a high-performance cathode material for Li-ion batteries

In this article, V₂O₅ with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V₂O₅ with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V₂O₅ electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g⁻¹ (at a current density of 100 mA g⁻¹) could be delivered and a stable discharge capacity of 240 mAh g⁻¹ after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.     

3D network-like porous MnCo2O4 by the sucrose-assisted combustion method for high-performance supercapacitors

3D network-like porous MnCo₂O₄ nanostructures have been successfully fabricated through a facile and scalable sucrose-assisted combustion route followed by calcination treatment. Benefiting from its advantages of the unique 3D network-like architectures with large specific surface area (216.15 m² g⁻¹), abundant mesoporosity (2–50 nm) and high electronic conductivity, the as-prepared MnCo₂O₄ electrode displays a high specific capacitance of 647.42 F g⁻¹ at a current density of 1 A g⁻¹, remarkable capacitance retention rate of 70.67% at current density of 10 A g⁻¹ compared with 1 A g⁻¹, and excellent cycle stability (only 6.32% loss after 3000 cycles). The excellent electrochemical performances coupled with facile and cost effective method will render the as-fabricated 3D network-like porous MnCo₂O₄ as a promising electrode material for supercapacitors.     

Exceptional electrochemical performance of nitrogen-doped porous carbon for lithium storage

Crumpled nitrogen-doped porous carbon sheets are successfully fabricated via chemical activation of polypyrrole-functionalized graphene sheets with KOH (APGs). The obtained APGs with nitrogen doping, high surface area, porous and crumpled structure exhibit exceptional electrochemical performances as the electrode material for LIBs, including a superhigh reversible specific capacity of 1516.2 mAh g⁻¹, excellent cycling stability over 10,000 cycles, and good rate capability (133.2 mAh g⁻¹ even at a very high current density of 40 A g⁻¹). The chemical activation synthesis strategy might open new avenues for the design of high-performance carbon-based anode materials.     

The effect of AlF3 modification on the physicochemical and electrochemical properties of Li-rich layered oxide

Lithium (Li)-rich layered oxides are considered promising cathode materials for Li-ion batteries because of their favorable properties. Here, we report our recent finding in the novel oxide, aluminum fluoride (AlF₃)-modified Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCAF), which was synthesized via a facile, cost-effective and readily scalable solid-state reaction. LMNCAF possess an F and Al co-doped core structure with a LiF nano-coating on its surface which leads to considerably enhancement in the electrochemical performance of the oxide. The initial discharge capacity (at 0.05 C) increased from 212 mA h g⁻¹ for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ to 291 mA h g⁻¹ for LMNCAF. A much higher discharge capacity of 211 mA h g⁻¹ was obtained for LMNCAF after 99 charge/discharge cycles at 0.2 C compared with that of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (160 mA h g⁻¹). Our preliminary results suggest that AlF₃ modification is an effective strategy to tailor the physicochemical and electrochemical properties of Li-rich layered oxides.     

Lithium insertion into dense and porous carbon-rich polymer-derived SiOC ceramics

Two polymer-derived SiOC ceramics with different amount of carbon were synthesized either as dense or porous SiOC powders. The dense materials were produced up to a maximum temperature of 1400 °C and show a phase separated nanostructure consisting of SiO₂-rich clusters, nanocrystalline SiC and nanocrystalline carbon phase. The corresponding porous materials were obtained by etching the silica phase of the dense SiOC with 20% HF solution. The electrochemical properties of the dense and porous SiOC ceramics in terms of lithium insertion/extraction were studied. Accordingly, the SiOC materials show a first lithium insertion capacity between 380 and 648 mAh g^?1 followed by significantly lower extraction capacities between 102 and 272 mAh g^?1. We consider the free carbon phase present in the ceramic as the major lithium intercalating agent. The porous samples show a stable electrochemical behavior up to 30 cycles while for the dense materials the efficiency drops to almost zero after 10 cycles.     

Nano-Y2O3-coated LiNi0.5Co0.2Mn0.3O2 cathodes with enhanced electrochemical stability under high cut-off voltage and high temperature

LiNi_0.5Co_0.2Mn_0.3O₂ (523) coated with ~ 20 nm thick Y₂O₃ nano-membrane is prepared via a sol-type chemical precipitation process based on electrostatic attraction between the materials. The nano-Y₂O₃-coated 523 cathode can deliver 160.3 mA h g⁻¹ (87.8% of its initial discharge capacity) after 50 cycles at 1 C (180 mA g⁻¹) between 3.0 and 4.6 V by coin cell testing, while the pristine 523 keeps only 146.2 mA h g⁻¹ with 78.6% capacity retention left. The capacity retention rate increases from 50% to 86.7% after 150 cycles at 1 C in 3.0–4.35 V by soft package testing under 45 °C. Through this novel Y₂O₃ coating operation, both the charge transfer resistance and the electrode polarization of the 523 electrode have been suppressed, and its structure stability is also improved.