Layer-Structured Ti Doped O3-Na1-xCr1-xTixO2(x=0, 0.03, 0.05) with Excellent Electrochemical Performance as Cathode Materials for Sodium Ion Batteries

Layer-structured O3 type cathode materials Na_1-xCr_1-xTi_xO₂(x=0, 0.03, 0.05) are fabricated by a thermo-polymerization method. The structures and morphologies are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. It has been found that the appropriate Ti doping effectively leads to the formation of uniform morphology. As a cathode, the x=0.03 sample delivers a quite high discharge capacity of 110 mAh/g at 32 C in the voltage range from 2.0 V to 3.6 V (vs. Na/Na⁺) and with a capacity retention of 96% after 100 cycles at 0.2 C. The Na//Na_0.97Cr_0.97Ti_0.03O₂ cell exhibits very high coulombic e ciency (above 96%). All these results suggest that Na_0.97Cr_0.97Ti_0.03O₂ is very promising for high-rate sodium ion batteries.     

High‐Entropy Layered Oxide Cathodes for Sodium‐Ion Batteries

Material innovation on high‐performance Na‐ion cathodes and the corresponding understanding of structural chemistry still remain a challenge. Herein, we report a new concept of high‐entropy strategy to design layered oxide cathodes for Na‐ion batteries. An example of layered O3‐type NaNi_0.12Cu_0.12Mg_0.12Fe_0.15Co_0.15Mn_0.1Ti_0.1Sn_0.1Sb_0.04O₂ has been demonstrated, which exhibits the longer cycling stability (ca. 83 % of capacity retention after 500 cycles) and the outstanding rate capability (ca. 80 % of capacity retention at the rate of 5.0 C). A highly reversible phase‐transition behavior between O3 and P3 structures occurs during the charge‐discharge process, and importantly, this behavior is delayed with more than 60 % of the total capacity being stored in O3‐type region. Possible mechanism can be attributed to the multiple transition‐metal components in this high‐entropy material which can accommodate the changes of local interactions during Na⁺ (de)intercalation. This strategy opens new insights into the development of advanced cathode materials.     

Electrode reactions of manganese oxides for secondary lithium batteries

Nanorods of MnO₂, Mn₃O₄, Mn₂O₃ and MnO are synthesized by hydrothermal reactions and subsequent annealing. It is shown that though different oxides experience distinct phase transition processes in the initial discharge, metallic Mn and Li₂O are the end products of discharge, while MnO is the end product of recharge for all these oxides between 0.0 and 3.0 V vs. Li⁺/Li. Of these 4 manganese oxides, MnO is believed the most promising anode material for lithium ion batteries while MnO₂ is the most promising cathode material for secondary lithium batteries.     

A Hydrostable Cathode Material Based on the Layered P2@P3 Composite that Shows Redox Behavior for Copper in High‐Rate and Long‐Cycling Sodium‐Ion Batteries

Low‐cost layered oxides free of Ni and Co are considered to be the most promising cathode materials for future sodium‐ion batteries. Biphasic Na_0.78Cu_0.27Zn_0.06Mn_0.67O₂ obtained via superficial atomic‐scale P3 intergrowth with P2 phase induced by Zn doping, consisting of inexpensive transition metals, is a promising cathode for sodium‐ion batteries. The P3 phase as a covering layer in this composite shows not only in excellent electrochemical performance but also its tolerance to moisture. The results indicate that partial Zn substitutes can effectively control biphase formation for improving the structural/electrochemical stability as well as the ionic diffusion coefficient. Based on in situ synchrotron X‐ray diffraction coupled with electron‐energy‐loss spectroscopy, a possible Cu^2+/3+ redox reaction mechanism has now been revealed.     

Synthesis of Single‐Crystalline Spinel LiMn2O4 Nanorods for Lithium‐Ion Batteries with High Rate Capability and Long Cycle Life

The long‐standing challenge associated with capacity fading of spinel LiMn₂O₄ cathode material for lithium‐ion batteries is investigated. Single‐crystalline spinel LiMn₂O₄ nanorods were successfully synthesized by a template‐engaged method. Porous Mn₃O₄ nanorods were used as self‐sacrificial templates, into which LiOH was infiltrated by a vacuum‐assisted impregnation route. When used as cathode materials for lithium‐ion batteries, the spinel LiMn₂O₄ nanorods exhibited superior long cycle life owing to the one‐dimensional nanorod structure, single‐crystallinity, and Li‐rich effect. LiMn₂O₄ nanorods retained 95.6 % of the initial capacity after 1000 cycles at 3C rate. In particular, the nanorod morphology of the spinel LiMn₂O₄ was well‐preserved after a long‐term cycling, suggesting the ultrahigh structural stability of the single crystalline spinel LiMn₂O₄ nanorods. This result shows the promising applications of single‐crystalline spinel LiMn₂O₄ nanorods as cathode materials for lithium‐ion batteries with high rate capability and long cycle life.     

Tunable lithium storage properties of metal lithium titanates by stoichiometric modulation

A simple stoichiometric modulation of Na_2 − 2xSr_xLi₂Ti₆O₁₄ was developed to achieve tunable electrochemical properties of the material. The concept was confirmed experimentally and theoretically using density functional theory (DFT) calculations. Both the operating potential and the amount of reversibly intercalated lithium ions were manipulated by simply changing the Na/Sr ratio. These unique characteristics originated from a gradual change in the electron density on the Ti atoms and the extra lithium insertion sites at SrLi₂Ti₆O₁₄. As a promising anode material for lithium-ion batteries, Na_2 − 2xSr_xLi₂Ti₆O₁₄ and its tunable electrochemical properties have significant importance in terms of the development of tailored electrodes with desirable electrochemical performance.     

Preparation and electrochemical lithium storage of flower-like spinel Li4Ti5O12 consisting of nanosheets

In this paper, flower-like spinel Li₄Ti₅O₁₂ consisting of nanosheets was synthesized by a hydrothermal process in glycol solution and following calcination. The as-prepared product was characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction and cyclic voltammetry. The capacity of the sample used as anode material for lithium ion battery was measured. This structured Li₄Ti₅O₁₂ exhibited a high reversible capacity and an excellent rate capability of 165.8 m Ahg⁻¹ at 8 C, indicating potential application for lithium ion batteries with high rate performance and high capacity.     

Ruthenium‐Oxide‐Coated Sodium Vanadium Fluorophosphate Nanowires as High‐Power Cathode Materials for Sodium‐Ion Batteries

Sodium‐ion batteries are a very promising alternative to lithium‐ion batteries because of their reliance on an abundant supply of sodium salts, environmental benignity, and low cost. However, the low rate capability and poor long‐term stability still hinder their practical application. A cathode material, formed of RuO₂‐coated Na₃V₂O₂(PO₄)₂F nanowires, has a 50 nm diameter with the space group of I4/mmm. When used as a cathode material for Na‐ion batteries, a reversible capacity of 120 mAh g^?1 at 1 C and 95 mAh g^?1 at 20 C can be achieved after 1000 charge–discharge cycles. The ultrahigh rate capability and enhanced cycling stability are comparable with high performance lithium cathodes. Combining first principles computational investigation with experimental observations, the excellent performance can be attributed to the uniform and highly conductive RuO₂ coating and the preferred growth of the (002) plane in the Na₃V₂O₂(PO₄)₂F nanowires.     

Influence of manganese ions dissolved from LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode on the degradation of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>-based lithium-ion batteries

A systematic investigation is conducted to evaluate the influence of dissolved manganese ions from LiMn₂O₄ cathode on the degradation of Li₄Ti₅O₁₂-based lithium-ion batteries. Worse capacity fading is found in Li₄Ti₅O₁₂-based full cells with increasing manganese ion addition. The interfacial film covered on Li₄Ti₅O₁₂ anode is affected by the manganese ion contamination during cycling, which becomes thicker but more non-uniform, and is composed by less ratio of compact components and more ratio of loose components compared with that free of contamination. Such flawed passivation film cannot restrain the further penetration of electrolyte and inhibit the contact between electrolyte and Li₄Ti₅O₁₂ anodes efficiently, thus triggering more interfacial reactions and that should be the reason for the more severe capacity degradation. Accordingly, we suggest that in addition to optimizing the chemistry and microstructure of Li₄Ti₅O₁₂ electrode, more attention should also be paid to minimizing the destructive effect imposed on the passivation film of Li₄Ti₅O₁₂ electrode by the transition metal ion contaminations.     

A redox‐active polythiophene‐modified separator for safety control of lithium‐ion batteries

A potential‐sensitive separator is prepared simply by incorporating a redox‐active poly(3‐butylthiophene) (P3BT) into the micropores of a commercial porous polyolefin film and tested for overcharge protection of LiFePO₄/Li₄Ti₅O₁₂ lithium‐ion batteries. The experimental results demonstrate that owing to the reversible p‐doping and dedoping of the redox‐active P3BT polymer embedded in the separator with the changes of the cathode potential from an overcharge state to a normal operating state, this type of separator can reversibly switch between electronically insulating state and conductive state to maintain the charge voltage of LiFePO₄/Li₄Ti₅O₁₂ cells at a safety value of ≤2.4 V, and thus protecting the cell from voltage runaway. As this type of the separators works reversibly and has no negative impact on the battery performances, it can be used as an internal and self‐protecting mechanism for commercial lithium‐ion batteries and other rechargeable batteries. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1487–1493     

Electrochemical properties of tetravalent Ti-doped spinel LiMn2O4

Ti-doped spinel LiMn₂O₄ is synthesized by solid-state reaction. The X-ray photoelectron spectroscopy and X-ray diffraction analysis indicate that the structure of the doped sample is Li( Mn^{3 +} Mn_{1 - x} ^{4 +} Ti_x^{4 +} )O₄ {\hbox{Li}}\left( {{\hbox{M}}{{\hbox{n}}^{3 + }}{\hbox{Mn}}_{1 - x\,}^{4 + }{\hbox{Ti}}_x^{4 + }} \right){\hbox{O}}{}_4 . The first principle-based calculation shows that the lattice energy increases as Ti doping content increases, which indicates that Ti doping reinforces the stability of the spinel structure. The galvanostatic charge–discharge results show that the doped sample LiMn_1.97Ti_0.03O₄ exhibits maximum discharge capacity of 135.7 mAh g⁻¹ (C/2 rate). Moreover, after 70 cycles, the capacity retention of LiMn_1.97Ti_0.03O₄ is 95.0% while the undoped sample LiMn₂O₄ shows only 84.6% retention under the same condition. Additionally, as charge–discharge rate increases to 12C, the doped sample delivers the capacity of 107 mAh g⁻¹, which is much higher than that of the undoped sample of only 82 mAh g⁻¹. The significantly enhanced capacity retention and rate capability are attributed to the more stable spinel structure, higher ion diffusion coefficient, and lower charge transfer resistance of the Ti-doped spinel.     

High-Entropy Layered Oxide Cathodes for Sodium-Ion Batteries

Material innovation on high-performance Na-ion cathodes and the corresponding understanding of structural chemistry still remain a challenge. Herein, we report a new concept of high-entropy strategy to design layered oxide cathodes for Na-ion batteries. An example of layered O3-type NaNi_0.12Cu_0.12Mg_0.12Fe_0.15Co_0.15Mn_0.1Ti_0.1Sn_0.1Sb_0.04O₂ has been demonstrated, which exhibits the longer cycling stability (ca. 83 % of capacity retention after 500 cycles) and the outstanding rate capability (ca. 80 % of capacity retention at the rate of 5.0 C). A highly reversible phase-transition behavior between O3 and P3 structures occurs during the charge-discharge process, and importantly, this behavior is delayed with more than 60 % of the total capacity being stored in O3-type region. Possible mechanism can be attributed to the multiple transition-metal components in this high-entropy material which can accommodate the changes of local interactions during Na⁺ (de)intercalation. This strategy opens new insights into the development of advanced cathode materials.     

A Cation and Anion Dual Doping Strategy for the Elevation of Titanium Redox Potential for High‐Power Sodium‐Ion Batteries

Titanium‐based polyanions have been intensively investigated for sodium‐ion batteries owing to their superior structural stability and thermal safety. However, their low working potential hindered further applications. Now, a cation and anion dual doping strategy is used to boost the redox potential of Ti‐based cathodes of Na₃Ti_0.5V_0.5(PO₃)₃N as a new cathode material for sodium ion batteries. Both the Ti³⁺/Ti⁴⁺ and V³⁺/V⁴⁺ redox couples are reversibly accessed, leading to two distinctive voltage platforms at ca. 3.3 V and ca. 3.8 V, respectively. The remarkably improved cycling stability (86.3 %, 3000 cycles) can be ascribed to the near‐zero volume strain in this unusual cubic symmetry, which has been demonstrated by in situ synchrotron‐based X‐ray diffraction. First‐principles calculations reveal its well‐interconnected 3D Na diffusion pathways with low energy barriers, and the two‐sodium‐extracted intermediate NaTi_0.5V_0.5(PO₃)₃N is also a stable phase according to formation energy calculations.     

Temporal evolution study of the plasma induced by CO2 pulsed laser on targets of titanium oxides

This paper reports studies on time-resolved laser induced breakdown spectroscopy (LIBS) of plasmas induced by IR nanosecond laser pulses on the titanium oxides TiO and TiO₂ (anatase). LIBS excitation was performed using a CO₂ laser. The laser-induced plasma was found strongly ionized yielding Ti⁺, O⁺, Ti^2 +, O^2 +, Ti^3 +, and Ti^4 + species and rich in neutral titanium and oxygen atoms. The temporal behavior of specific emission lines of Ti, Ti⁺, Ti^2 + and Ti^3 + was characterized. The results show a faster decay of Ti^3 + and Ti^2 + ionic species than that of Ti⁺ and neutral Ti atoms. Spectroscopic diagnostics were used to determine the time-resolved electron density and excitation temperatures. Laser irradiation of TiO₂-anatase induces on the surface sample the polymorphic transformation to TiO₂-rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy.     

Spinel LiNi0.5Mn1.5O4 and its derivatives as cathodes for high-voltage Li-ion batteries

The spinel material LiNi_0.5Mn_1.5O₄ displays a remarkable property of high charge/discharge voltage plateau at around 4.7 V. It is a promising cathode material for new-generation lithium-ion batteries with high voltage. Recently, a lot of researches related to this material have been carried out. In this review we present a summary of these researches, including the structure, the mechanism of high voltage, and the latest developments in improving its electrochemical properties like rate ability and cycle performance at elevated temperature, etc. Doping element and synthesizing nanoscale material are effective ways to improve its rate ability. The novel battery systems, like LiNi_0.5Mn_1.5O₄/Li₅Ti₄O₁₂ with good electrochemical properties, are also in progress.     

Effect of Li2O Addition on the Preparation of (Y2‐yLiy)Ti2O7‐y

A new series of (Y_2‐yLi_y)Ti₂O_7‐y having an ordered pyrochlore phase was prepared by a solid state reaction method with a solid solution range of 0.05 ≥ y ≥ 0.10. Unit cell parameters obtained by the Rietveld refinement method shows that the a‐axis decreases linearly with increasing the amount of Li ion addition, indicating the successful incorporation of the Li ion into unit cell. The average x‐fractional coordinate of the O(1) site depends on the ionic radius ratio of r(A³+)/r(Ti⁴⁺) in the A₂Ti₂O₇ with a pyrochlore phase. The Ti K‐edge XANES spectra of the (Y_2‐yLi_y)Ti₂O_7‐y show that the valence of the Ti ions is slightly less than 4 so that Ti is in the mixed valence state. Average particle size increases with increasing the amount of extra Li ion addition, which acts as a flux to lower the melting point of the materials.     

High-performance thin-film Li4Ti5O12 electrodes fabricated by using ink-jet printing technique and their electrochemical properties

Li₄Ti₅O₁₂ thin-film anode with high discharge capacity and excellent cycle stability for rechargeable lithium ion batteries was prepared successfully by using ink-jet printing technique. The prepared Li₄Ti₅O₁₂ thin film were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammograms, and galvanostatic charge–discharge measurements. It was found that the average thickness of 10-layer Li₄Ti₅O₁₂ film was about 1.7~1.8 μm and the active material Li₄Ti₅O₁₂ in the thin film was nano-sized about 50–300 nm. It was also found that the prepared Li₄Ti₅O₁₂ thin film exhibited a high discharge capacity of about 174 mAh/g and the discharge capacity in the 300th cycle retained 88% of the largest discharge capacity at a current density of 10.4 μA/cm² in the potential range of 1.0–2.0 V.     

Sol–gel preparation and electrochemical properties of La-doped Li4Ti5O12 anode material for lithium-ion battery

A sol–gel method using Ti(OC₄H₉)₄, LiCH₃COO·2H₂O, and La(NO₃)₃·6H₂O as starting materials and ethyl acetoacetate as chelating agent to prepare pure and lanthanum (La)-doped Li₄Ti₅O₁₂ is reported. The structure and morphology of the active materials characterized by powder X-ray diffraction and scanning electron microscopy analysis indicate that doping with a certain amount of La³⁺ does not affect the structure of Li₄Ti₅O₁₂, but can restrain the agglomeration of the particles during heat treatment. The electrochemical properties measured by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling tests show that La-doped Li₄Ti₅O₁₂ presents a much improved electrochemical performance due to a decrease in charge transfer resistance. At current densities of 1 and 5 C, the La-doped Li₄Ti₅O₁₂ exhibits excellent reversible capacities of 156.16 and 150.79 mAh?g^?1, respectively. The excellent rate capability and good cycling performance make La-doped Li₄Ti₅O₁₂ a promising anode material for lithium-ion batteries in energy storage systems.     

Template‐Free Synthesis of Hierarchical Vanadium‐Glycolate Hollow Microspheres and Their Conversion to V2O5 with Improved Lithium Storage Capability

Nanosheet‐assembled hierarchical V₂O₅ hollow microspheres are successfully obtained from V‐glycolate precursor hollow microspheres, which in turn are synthesized by a simple template‐free solvothermal method. The structural evolution of the V‐glycolate hollow microspheres has been studied and explained by the inside‐out Ostwald‐ripening mechanism. The surface morphologies of the hollow microspheres can be controlled by varying the mixture solution and the solvothermal reaction time. After calcination in air, hierarchical V₂O₅ hollow microspheres with a high surface area of 70 m² g^?1 can be obtained and the structure is well preserved. When evaluated as cathode materials for lithium‐ion batteries, the as‐prepared hierarchical V₂O₅ hollow spheres deliver a specific discharge capacity of 144 mA h g^?1 at a current density of 100 mA g^?1, which is very close to the theoretical capacity (147 mA h g^?1) for one Li⁺ insertion per V₂O₅. In addition, excellent rate capability and cycling stability are observed, suggesting their promising use in lithium‐ion batteries.     

Efforts towards Practical and Sustainable Li/Na‐Air Batteries

The Li‐O₂ batteries have attracted much attention due to their parallel theoretical energy density to gasoline. In the past 20 years, understanding and knowledge in Li‐O₂ battery have greatly deepened in elucidating the relationship between structure and performance. Our group has been focusing on the cathode engineering and anode protection strategy development in the past years, trying to make full use of the superiority of metal‐air batteries towards applications. In this review, we aim to retrospect our efforts in developing practical, sustainable metal‐air batteries. We will first introduce the basic working principle of Li‐O₂ batteries and our progresses in Li‐O₂ batteries with typical cathode designs and anode protection strategies, which have together promoted the large capacity, long life and low charge overpotential. We emphasize the designing art of carbon‐based cathodes in this part along with a short talk on all‐metal cathodes. The following part is our research in Na‐O₂ batteries including both cathode and anode optimizations. The differences between Li‐O₂ and Na‐O₂ batteries are also briefly discussed. Subsequently, our proof‐of‐concept work on Li‐N₂ battery, a new energy storage system and chemistry, is discussed with detailed information on the discharge product identification. Finally, we summarize our designed models and prototypes of flexible metal‐air batteries that are promising to be used in flexible devices to deliver more power.