Reduced Electrode Polarization Research Articles

Manufacturability of bolt-microtubular anode supports for solid oxide fuel cells

The effects of anode support tape length on the manufacturability and level of surface patterning in bolt-microtubular anode supports (BMASs) for solid oxide fuel cells (SOFCs) are investigated in this study. Continuous anode support tapes of ∼5–25 cm are wrapped on a threaded rod for this purpose and five-layered bolt-microtubular cells (BMCs) are manufactured on these supports. Similarly, microtubular anode supports (MASs) by using a pin and corresponding microtubular cells (MCs) are also fabricated and examined for comparison. The tape lengths ≤9.9 cm yield mechanically unstable BMASs or BMSs due to fractures that occur during sintering in the anode supports or during testing in the cells. The electrochemical performance tests show that all BMCs exhibit relatively higher performances compared to those of MCs for a certain tape length. The highest maximum power density of 0.479 Wcm−2 at 800 °C operating temperature is obtained from BMC prepared with 12 cm long anode support tape, whereas that of MC fabricated with the same anode support length is measured as 0.313 Wcm2 under the same testing conditions. The impedance measurements reveal that the improvement in the cell performances is due to reduced electrode polarization resistance achieved by the bolt-like microtube design.

Trinary nanogradients at electrode/electrolyte interface for lean zinc metal batteries

Zn2+ ion transport kinetics is limited by the insufficient electrochemically active surface area of planar Zn metal. Although the three-dimensional (3D) framework homogenizes local current density and hence reduces electrode polarization, its interface lacks the incorporation of affinity sites and the regulation of active water molecules. Herein, we constructed the nanopore structure on the copper foam framework to prepare a 3D electrode with trinary nanogradients (TNGs) including conductivity-dielectric, zincophilicity, and electrolyte concentration. The conductivity-dielectric and zincophilicity gradients enable the bottom-up growth of Zn metal in the surface mesopores by altering the distribution electric field. In addition, the electrolyte adsorbed in the mesopores forms a type of water-poor, Zn-rich "reservoirs" by interacting with the functional groups on the pore wall, thereby forming a concentration gradient with the electrolyte outside and limiting the number of active water molecules. The TNGs can achieve reversible plating/stripping with an average Coulombic Efficiency (CE) of 99.5% over 3000 cycles. Finally, a full battery (N/P ratio≈2.5) with a 3D lean-zinc anode and NH4V4O10 as the cathode was assembled, which can be cycled stably for 500 cycles (2 A g-1). We hope that such a 3D framework design with trinary nanogradients will open up a new avenue for improving the practicality of zinc metal anodes.

Feasibility study of applying a graphene oxide-alginate composite hydrogel to electrokinetic remediation of Cu(II)-contaminated loess as electrodes

Inappropriate handling of heavy metal-containing wastewater resulting from extensive mining and smelting activities causes serious threats to surrounding environments and human health. The electrokinetic (EK) technology has been extensively applied to remediate heavy metal-contaminated sites because of its great manoeuvrability. The electrochemical polarization effect, however, reduces the electron transfer rate and could badly degrade EK removal efficiency. To this end, the present work proposed a novel graphene oxide-alginate composite hydrogel and applied it to copper removal as electrodes in EK remediation. A series of laboratory tests concerning its physical, mechanical, adsorption, and electrochemical properties were conducted. The graphene oxide (GO) particles provide larger average pore size and pore volume than traditional activated carbon electrodes. The surface functional groups, including hydroxyl, carboxyl, and epoxide groups, promote hydrogen bond formation. The GO particles and the calcium alginate are crosslinked with the hydrogen bonds, improving the mechanical properties of the graphene oxide-alginate composite hydrogel. Furthermore, the functional groups also encourage copper adsorption, and a high GO proportion does not necessarily mean an improvement in copper adsorption. The dynamic mechanism of Cu(II) adsorption onto the graphene oxide-alginate composite hydrogel conforms with the pseudo-second-order kinetic model. Moreover, the absence of oxidative and reductive peaks in the cyclic voltammograms is mainly attributed to the non-faradaic nature of the graphene oxide-alginate composite hydrogel, indicating a reduced electrode polarization effect. The Nyquist plot also approves its low resistance nature. The results were then compared against other electrodes to highlight the relative merits of the proposed graphene oxide-alginate composite hydrogel electrode.

Temperature effects on electrochemical performance of Li4Ti5O12

Li4Ti5O12(LTO) is one of the most popular [Formula: see text]-storage anode materials. However, the influences of different operating temperatures on the electrochemical performance of LTO and the underlying mechanisms are still unclear. Herein, we systematically investigate its temperature-dependent electrochemical performance, electrochemical kinetics, and crystal-structural evolution at −10[Formula: see text]C, [Formula: see text]C, [Formula: see text]C, [Formula: see text]C, and [Formula: see text]C. When the operation temperature increases from −10[Formula: see text]C to [Formula: see text]C, more intensive electrolyte decomposition increases the irreversible capacity in the first cycle, which decreases the initial Coulombic efficiency. Meanwhile, the electrochemical kinetics becomes faster, leading to reduced electrode polarization, faster [Formula: see text]Transport, and higher rate capability. Finally, the maximum unit-cell-volume shrinkage enlarges, resulting in the decay of the cyclic stability. However, when the temperature further rises to 60°C, the rate capacity and cyclic stability rapidly decay due to the severe electrolyte decomposition catalyzed by [Formula: see text] and the formation of thick solid electrolyte interface (SEI) films.

Aqueous Binders Compatible with Ionic Liquid Electrolyte for High-Performance Aluminum-Ion Batteries.

The incompatibility of poly(vinylidene difluoride) (PVDF) with acidic ionic liquid electrolytes and the use of toxic and high-cost N-methyl pyrrolidone (NMP) solvents hinder the wide application of aluminum-ion batteries (AIBs). In this work, sodium alginate (Na-Alg) is developed as an aqueous binder for the fabrication of graphite positive electrodes in AIBs. The compatibility of various binders with the ionic liquid electrolyte is evaluated, and interaction between various binders and graphite particles before and after cycling is compared and discussed. The results demonstrate that the well compatibility of Na-Alg in ionic liquids and its reasonable distribution on the graphite surface facilitate fast charge transfer and ion diffusion, reduce electrode polarization, and thus contributing to significantly improved cycling stability and rate capability of AIBs. This work provides a new insight into the development of low-cost, eco-friendly, and high-performance binders for AIBs.

FeF3·0.33H2O@C nanocomposites derived from pomegranate structure as high-performance cathodes for sodium- and lithium-ion batteries

Iron fluoride is an excellent cathode material for alkali metal-ion batteries due to its high operating voltage and extremely high specific discharge capacity. To overcome its voltage hysteresis and compensate for capacity fading due to volume change and electrode dissolution, a FeF3·0.33H2O@carbon nanocomposite with a pomegranate-like structure (FeF3·0.33H2O@C) is designed and successfully synthesized via hydrothermal synthesis followed by a solid-phase process. The FeF3·0.33H2O@C nanocomposite derived from pomegranate structure effectively can reduce electrode polarization via its unique hierarchical carbon-coated architecture. Additionally, combining other structural advantages (e.g., coordination of volume expansion, reduction of Fe dissolution, and inhibition of nanoparticle coarsening) can result in high reversibility and rate performance. For Lithium-ion battery, the nanocomposite cathode demonstrates a discharging capacity of 225 mA h g−1 at 0.1C, as well as an excellent long-cycle performance with a capacity retention rate of 93% after 200 cycles. When the cathode materials are used in sodium-ion batteries, the nanocomposite cathode achieves an exceptionally high energy density of 1015 Wh kg−1, which is more than twice that of the commercial LiCoO2 cathode (504 Wh kg−1).

Enhanced electrochemical performance of Li4Ti5O12 anode material by LaF3 surface modification for lithium-ion batteries

The LaF3-modified Li4Ti5O12 materials have been synthesized via a chemical co-precipitation method, and the effects of different amounts of LaF3 modification (0.5 wt%, 1 wt%, 2 wt%, and 3 wt%) on the morphology, structure, and electrochemical performance of the Li4Ti5O12 (LTO) materials were investigated. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) characterizations show that the La3+ or F− ions are not incorporated into the LTO particles, and major LaF3 and minor La2O3 peaks are observed in the LaF3-modified LTO samples. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the generated LaF3/La2O3 nanoparticles are continuously wrapped around the surfaces of LTO particles. Charge-discharge tests reveal that the 1 wt% LaF3-modified LTO material (1LaFLTO) exhibits the highest rate capacity values among all of the samples of 199.9, 187.4 and 159.7 mAh g−1 at 3C, 5C, and 10C, respectively between 0 and 3 V. Moreover, 1LaFLTO also delivers superior cycling stability with a capacity retention of 94.5% after 300 cycles at 5C between 1 and 3 V. The electrochemical results demonstrate that the appropriate LaF3/La2O3 nanoparticles coated on the surface of 1LaFLTO particles not only reduce electrode polarization, SEI film resistance, and charge-transfer resistance but also accelerate Li+ diffusion and improve the reversibility, which is favorable for enhancing the electrochemical performance of LTO material.

In situ Sr2+-doped spinel LiNi0.5Mn1.5O4 cathode material for Li-ion batteries with high electrochemical performance and its impact on morphology

LiNi0.5Mn1.5O4 (LNMO) is a promising next-generation cathode material for high energy density lithium-ion batteries, but the application of LNMO is blocked because of its inherent side effects with electrolytes at high voltages, namely, serious Mn dissolution and capacity attenuation. A novel LiNi0.5Mn1.5-xSrxO4 material (x = 0, 0.05, 0.1, 0.15, and 0.2) was successfully prepared using the sol-gel method, and the effect of varying in situ Sr2+-doping on the crystal structure, morphology, and electrochemical performance was researched. A series of characterizations showed that the Sr-doped LNMO structure contains less Mn3+, which enhances its cycling stability. In addition, Sr doping promotes morphological changes more remarkably. Accompanied by the appearance of (100) surfaces, the morphology of LNMO changes from an octahedron to a truncated octahedron. The (100) surface can effectively inhibit side reactions with the electrolyte and steady the structure at the working voltage, which also helps support Li+ transport kinetics. The Sr-doped LiNi0.5Mn1.4Sr0.1O4 (expressed as LNMO-Sr0.1) cathode exhibits preeminent cycling stability, after 500 cycles at 1C, the capacity retention is 86.63 %. CV and EIS results show that the right amount of Sr doping efficiently reduces electrode polarization and charge transfer resistance and increases the Li+ diffusion coefficient.

Enhancing the Capacity and Stability by CoFe2O4 Modified g-C3N4 Composite for Lithium-Oxygen Batteries.

As society progresses, the task of developing new green energy brooks no delay. Li-O2 batteries have high theoretical capacity, but are difficult to put into practical use due to problems such as high overvoltage, low charge-discharge efficiency, poor rate, and cycle performance. The development of high-efficiency catalysts to effectively solve the shortcomings of Li-O2 batteries is of great significance to finding a solution for energy problems. Herein, we design CoFe2O4/g-C3N4 composites, and combine the advantages of the g-C3N4 material with the spinel-type metal oxide material. The flaky structure of g-C3N4 accelerates the transportation of oxygen and lithium ions and inhibits the accumulation of CoFe2O4 particles. The CoFe2O4 materials accelerate the decomposition of Li2O2 and reduce electrode polarization in the charge–discharge reaction. When CoFe2O4/g-C3N4 composites are used as catalysts in Li-O2 batteries, the battery has a better discharge specific capacity of 9550 mA h g−1 (catalyst mass), and the cycle stability of the battery has been improved, which is stable for 85 cycles.

Promoting the Li storage performances of Li2ZnTi3O8@Na2WO4 composite anode for Li-ion battery

In this work, a reasonable strategy for the construction of Li2ZnTi3O8@Na2WO4 composite was employed to promote the Li storage performances of Li2ZnTi3O8. The Li2ZnTi3O8@Na2WO4 composites (5, 10, and 15 wt%) were then prepared by a solution dispersion method. The introduction of Na2WO4 does not change the structures of the samples and they show similar morphologies with particle sizes from 100 to 200 nm. Suitable amount of Na2WO4 modification effectively improves the electrochemical performance of Li2ZnTi3O8. Li2ZnTi3O8@Na2WO4 composites (0, 5, 10, and 15 wt%) deliver the discharge/charge capacities of 137.4/136.4, 164.2/162.3, 189.2/188.1, and 154.5/153.3 mAh g−1 at 0.5 A g−1 after 100 cycles, respectively. Li2ZnTi3O8@Na2WO4 composites (10 wt%) has the highest reversible capacities among all samples. The Na2WO4 shell with an excellent electronic conductivity can reduce electrode polarization, decrease the charge transfer resistance, enhance the Li-ion diffusion coefficient of Li2ZnTi3O8, and then improve the electrochemical kinetics of composites. In addition, the formation of Ti–O bonds at the interface can be helpful for the stabilization of the composite, being beneficial for the improvement of their cycling stabilities. These results reveal that Na2WO4 coating is a facile and effective strategy to promote the Li storage performance of Li2ZnTi3O8.

Optimization mechanism of Li2ZrO3-modified lithium-rich cathode material Li[Li0.2Ni0.2Mn0.6]O2 for lithium-ion batteries

To achieve lithium-ion batteries with high energy and power density, it is necessary to develop alternative high-capacity cathode materials for traditional LiCoO2 or LiFePO4, such as lithium-rich manganese-based cathode materials. However, there are still some practical problems that Li-rich materials need to be further improved, such as structure transformation issue and poor rate capability. Here, the modification of Li[Li0.2Ni0.2Mn0.6]O2 cathode material by lithium-ion conductor (Li2ZrO3) has been achieved by a sol–gel method, and the optimization mechanism is preliminarily explored. The first charge/discharge specific capacities of the modified material coated with 1 wt.% Li2ZrO3 can reach 272.1 and 196.1 mAh g− 1 at 0.5 C, which are obviously higher than those of the pristine material. The rate capability has also been improved at 2 C and 5 C. As a fast lithium-ion conductor with good chemical stability, Li2ZrO3 material can form a continuous and uniform coating layer on the surface of active particles, which can inhibit the side reaction between the electrolyte and the electrode material, effectively prevent the corrosion of cathode material by HF attack, and reduce electrode polarization at high rates, leading to the improvement of the specific capacity and the structure stability of Li-rich material.

Electrochemical performance of in situ LiFePO4 modified by N-doped graphene for Li-ion batteries

LiFePO4 modified by N-doped graphene (NG) with a three-dimensional conductive network structure was synthesized via a one-step in situ hydrothermal method. The effects of N amount of NG on the phase structure, morphology, and electrochemical properties of LiFePO4 are investigated in this study. X-ray diffraction (XRD) results show that doping suitable N amounts in NG do not alter the crystal structure of LiFePO4, and scanning electron microscopy (SEM) images show that NG can slightly reduce the particle size of LiFePO4. The high-resolution transmission electron microscopy (HRTEM) results show that the LiFePO4 particles are well covered and connected by NG. The electrochemical performance confirms that LiFePO4 modified by 20% N-doped graphene (named LFP/NG-4) displays a perfect specific capacity of 166.6 mAh·g−1 at a rate of 0.2C and can reach 125 mAh·g−1 at a rate of 5 C. Electrochemical impedance spectroscopy (EIS) results illustrate that the charge transfer resistance value of the LFP/NG-4 composite is only 58.6 Ω, which is very low compared with LiFePO4. Cyclic voltammetry (CV) tests indicate that the addition of 20% N-doped graphene can effectively reduce electrode polarization and improve reversibility. The LFP/NG-4 composite with a three-dimensional conductive network structure can be regarded as a promising cathode material for Li-ion batteries.

High performance of phosphorus and fluorine co-doped LiNi0.8Co0.1Mn0.1O2 as a cathode material for lithium ion batteries

LiNi0.8Co0.1Mn0.1O2 (NCM811) is one of the promising cathode materials for high energy lithium ion batteries (LIBs). However, there is still ample room to improve its cycling stability. Herein, LiPF6 has been smartly employed as a doping agent to realize the P and F codoping into the structure of NCM811 material. As a result, the d-spacing of the material was enlarged, which facilitated the Li+ ions insersion/deinsersion, and the surface of NCM811 particles was stabilized as well. Thus, the cycling performance of the NCM811 material was effectively improved, although slightly lowered the initial capacity. After 100 cycles, capacity retention rates of 88.8% (159.5 mAh g−1) and 94.4% (162.3 mAh g−1) were achieved at 0.5C for doped NCM811 samples by 0.5 wt% and 1 wt% LiPF6 solution, respectively, which is much higher compared with that of the pristine NCM811 (77.7%, 143.6 mAh g−1). Similar trend has also been obtained at 1 C, in that, the 0.5% sample has the optimum capacity enhancement of 87.6%. The improved cycling stability is attributed to the enhanced reversibility of Li+ intercalation/deintercalation and reduced electrode polarization, due to the P and F codoping. Overall, the P and F codoped NCM811 material is promising for high energy LIBs application as a cathode material.

Reduced electrode polarization at electrode and analyte interface in impedance spectroscopy using carbon paste and paper.

The double layer present at the interface of an electrode and an analyte causes electrode polarization (EP) in impedance spectroscopy, which hinders acquiring the actual impedance of biological samples at a lower frequency region. In this work, a novel carbon paste (CP) electrode material prepared by mixing the pencil graphite powder with transparent glue has been reported to reduce the EP by depositing its two coplanar electrodes on a chromatography paper substrate. Furthermore, two other devices having silver paste and pencil electrodes on the chromatography paper have been fabricated, analyzed for the EP, and compared with the CP electrode. The EP is quantified by fitting the impedance data to an equivalent electrical circuit having double layer capacitance as a constant phase element, and the CP electrode shows the lowest EP among the electrodes. The cyclic voltammetry analysis reveals blocking electrode property of the CP, which diminishes dc current flow at the electrode/electrolyte interface. Furthermore, the chromatography paper is found to increase the effective surface area of the deposited electrode by enhancing its surface roughness, which helps reduce the EP.

Shape-controlled growth of three-dimensional flower-like ZnO@Ag composite and its outstanding electrochemical performance for Ni-Zn secondary batteries

A novel three-dimensional (3D) flower-like ZnO@Ag composite is successfully synthesized through a simple and facile process, which is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).When evaluated as an anodic material for nickel-zinc alkaline secondary batteries, the 3D flower-like ZnO@Ag composite exhibits the high discharge capacity (627 mAh g−1) and long cycle life (830 cycles). The outstanding electrochemical performance is ascribed to the Ag nanoparticles enhancing electron conductivity and the uniform flower-like structure providing enough electrochemical reaction sites, so as to reduce electrode polarization and improve cell efficiency. Furthermore, the possible growth mechanism of 3D flower-like ZnO@Ag composite has been proposed. The effect of silver content on formation of ZnO@Ag composites was also investigated in detail, indicating the appropriate silver content plays a key role in forming a defined 3 D flower-like structure for the ZnO@Ag composite.

Effects of Ag coating on the structural and electrochemical properties of LiNi0.8Co0.1Mn0.1O2 as cathode material for lithium ion batteries

Ni-rich layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode materials are synthesized using Ni0.8Co0.1Mn0.1(OH)2 precursors obtained from a co-precipitation reaction and then coated with of metal Ag for the first time. X-ray diffraction results verify that Ag+ ions can hardly dope into the bulk NCM811 particles and the ion mixing degree of Li+/Ni2+ has been reduced. Amorphous Ag coating layers formed on the surface of Ag coated NCM811 materials are proved by scanning electron microscope and transmission electron microscope. X-ray photoelectron spectroscopy demonstrates that more Ni3+ ions on the surface of Ag coated NCM811 materials than that of pure NCM811. Galvanostatic charge-discharge tests indicate that 1 wt% Ag coated NCM811 exhibits initial discharge capacity of 209.1 mAh·g−1 and superior capacity retention of 90.5% after 90 cycles between 2.8 and 4.3 V, which shows greatly improved cycling stability compared with the pure NCM811 (87.9%). After Ag coating, reduced electrode polarization is certified by cyclic voltammetry, and better electron conductivity and higher Li+ diffusion coefficient are testified by electrochemical impedance spectroscopy. These results clearly indicate Ag coating can enhance the structural and electrochemical properties of NCM811 materials.

Study of phase stability of SrTi0.3Fe0.7O3−δ perovskite in reducing atmosphere: Effect of microstructure

Increasing SOFC electrode's surface area by modification of its microstructure is a well-known technique to reduce electrode polarization resistance. This is because reduced grain size and increased porosity promote diffusion and surface reactions, thus improving the electrode performance. However, a modified microstructure also causes differences in phase stability and in chemical compatibility with other SOFC materials.In this work, we study the effect of particle size in both the electrode performance and the phase stability under different fuel conditions and temperatures. SrTi0.3Fe0.7O3−δ (STF) is both prepared via solid state reaction (STF-SSR) and also by an alternative sol-gel route (STF-SG). The sintering temperature is reduced dramatically with the sol-gel method, hence inducing a higher porosity and a much smaller grain size. As particle size is reduced the stability under fuel conditions is also diminished, so decomposition induced by segregation of metallic Fe and SrO occurs at lower temperatures for the STF-SG sample. The stability under reducing conditions is studied by combined techniques such as TGA, TPR, XRD, SEM and TEM. Performance as anode and cathode is evaluated by Electrochemical Impedance Spectroscopy (EIS) by using electrolyte supported symmetrical cells. Prior to electrochemical experiments, the reactivity between La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) electrolyte and STF was studied, and also between STF and a Lanthanum Doped Ceria (LDC) buffer layer. It is seen that microstructure also plays a key role in the chemical stability of the STF. The impact of particle size reduction is higher for the anodic polarization resistance, which is reduced twice from STF-SSR to STF-SG.

Design guidelines for the manufacturing of the electrode-electrolyte interface of solid oxide fuel cells

The advent of 3D printing has ushered in the scope for designing microstructures for solid oxide fuel cells (SOFCs) with enhanced power density and lifetime. Additive manufacturing can introduce structural modifications such as dense electrolyte pillars embedded within the porous electrode domain to facilitate ion transport. This study presents comprehensive guidelines to the design of electrolyte pillars to minimize the polarization resistance and increase the electrode robustness by means of a numerical model comprising electrochemical phenomena and structural mechanics. Numerical results show that the introduction of rectangular and trapezoidal pillars can reduce electrode polarization provided that an electrode thickness larger than the active thickness is used. Lateral fins or any protrusions sticking out the pillar hinder gas transport and should be avoided. Mechanical stress, up to twice the external compressive load, accumulates at the pillar/electrolyte junction, indicating that sharp corners must be smoothed during pillar manufacturing. Additional considerations regarding the fabrication accuracy and minimum resolution are addressed too. Although a simple and general recipe for the optimal electrode fabrication is not possible, the rationale behind the strategies for the best pillar design are presented and critically discussed.

Nanosized Fe7S8 with high surface area as polysulfide capturer combined with graphene for Li–S battery cathode

Lithium-sulfur (Li–S) battery system shows immense potential as energy storage devices with high energy density. However, the soluble property of polysulfides into the electrolyte during charge/discharge process leads to low sulfur utilization, severe polarization and short cyclic life, which has been a serious obstacle for practical application. How to anchor the polysulfides onto the cathode materials and moreover, enhance its further conversion to the final products, have been important challenges for the utilization of Li–S batteries. Herein, a novel well crystallized nanosized Fe7S8 possessing of a high specific surface area of 55.6 m2 g−1 fabricated by a simple microwave-assisted method combined with high temperature pyrolysis technique, is introduced into the S/C composite cathode for the first time. Strong interaction between polysulfides and the Fe7S8 can be realized to relieve the shuttle effect. The redox reaction of polysulfides can also be promoted to reduce electrode polarization. As a result of the enhanced utilization of sulfur, the optimized S@GFS-15 electrode may deliver a high initial discharge capacity of 1307.2 mA h g−1 at 0.1 C (1 C = 1675 mA h g−1) and low decay rates of 0.047% and 0.037% per cycle after 1000 cycles at 1 and 2 C respectively when the sulfur loading is ordinary 1.1 mg cm−2. Even the sulfur loading rises up to 2.6 mg cm−2, a large initial discharge specific capacity of 1134.5 mA h g−1 can be achieved at 0.1 C. After 600 cycles, the specific capacity of 457.3 mA h g−1 with a relatively small average decay rate of 0.062% per cycle can be obtained. Thus, incorporation of the nanosized Fe7S8 with graphene can help to achieve effective performance improvement route for Li–S batteries.

Al-Ti-oxide coated LiCoO2 cathode material with enhanced electrochemical performance at a high cutoff charge potential of 4.5 V

In this work, Al-Ti-oxide coated LiCoO2 material is synthesized by a one-step solid-state reaction and then coated with Al-Ti-oxide via a wet chemical method. X-ray photoelectron spectroscopy results indicate that, for the Al-Ti-oxide coated LiCoO2 material, Al3+ is partly doped into the host structure near the surface; however, Ti4+ is hardly incorporated into the bulk structure of LiCoO2. In addition, the amorphous Al-Ti-oxide coating layer on the surface of the Al-Ti-oxide coated LiCoO2 material is proved by scanning electron microscopy, scanning transmission electron microscopy and high-angle annular dark-field imaging with energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Electrochemical tests verify that the Al-Ti-oxide coated LiCoO2 material achieves a discharge capacity of 180.1 mAh g−1 after 100 cycles in the range 3.0–4.5 V at a rate of 1C (1C = 177.5 mAh g−1), with a high retention up to 96.9%, suggesting outstanding high-voltage and -rate performance. The enhanced electrochemical property of the Al-Ti-oxide coated LiCoO2 material can be ascribed to the reduced electrode polarization and improved electronic and ionic conductivities by the Al-Ti-oxide coating process. Thus, an easy and feasible method of improving the electrochemical performance of a LiCoO2 cathode at a high cutoff charge potential for industrialization is provided.