Ab initio Studies on Li4+xTi5O12 Compounds as Anode Materials for Lithium‐Ion Batteries

The structural and electronic properties of Li_4+xTi₅O₁₂ compounds (with 0≤x≤6)—to be used as anode materials for lithium‐ion batteries—are studied by means of first principles calculations. The results suggest that Li₄Ti₅O₁₂ can be lithiated to the state Li_8.5Ti₅O₁₂, which provides a theoretical capacity that is about 1.5 times higher than that of the compound lithiated to Li₇Ti₅O₁₂. Further insertion of lithium species into the Li_8.5Ti₅O₁₂ lattice results in a clear structural distortion. The small lattice expansion observed upon lithium insertion (about 0.4 % for the lithiated material Li_8.5Ti₅O₁₂) and the retained [Li₁Ti₅]^16dO₁₂ framework indicate that the insertion/extraction process is reversible. Furthermore, the predicted intercalation potentials are 1.48 and 0.05 V (vs Li/Li⁺) for the Li₄Ti₅O₁₂/Li₇Ti₅O₁₂ and Li₇Ti₅O₁₂/Li_8.5Ti₅O₁₂ composition ranges, respectively. Electronic‐structure analysis shows that the lithiated states Li_4+xTi₅O₁₂ are metallic, which is indicative of good electronic‐conduction properties.     

Structural and Electrochemical Study of Vanadium‐Doped TiO2 Ramsdellite with Superior Lithium Storage Properties for Lithium‐Ion Batteries

Titanium‐oxide‐based materials are considered attractive and safe alternatives to carbonaceous anodes in Li‐ion batteries. In particular, the ramsdellite form TiO₂(R) is known for its superior lithium‐storage ability as the bulk material when compared with other titanates. In this work, we prepared V‐doped lithium titanate ramsdellites with the formula Li_0.5Ti_1?xV_xO₂ (0≤x≤0.5) by a conventional solid‐state reaction. The lithium‐free Ti_1?xV_xO₂ compounds, in which the ramsdellite framework remains virtually unaltered, are easily obtained by a simple aqueous oxidation/ion‐extraction process. Neutron powder diffraction is used to locate the Li channel site in Li_0.5Ti_1?xV_xO₂ compounds and to follow the lithium extraction by difference‐Fourier maps. Previously delithiated Ti_1?xV_xO₂ ramsdellites are able to insert up to 0.8 Li⁺ per transition‐metal atom. The initial gravimetric capacities of 270 mAh g^?1 with good cycle stability under constant current discharge conditions are among the highest reported for bulk TiO₂‐related intercalation compounds for the threshold of one e^? per formula unit.     

Mesoporous Spherical Li4Ti5O12 as High‐Performance Anodes for Lithium‐Ion Batteries

Porous microspherical Li₄Ti₅O₁₂ aggregates (LTO‐PSA) can be successfully prepared by using porous spherical TiO₂ as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO‐PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO‐PSA at 30 C is as high as 141 mA h g^?1, whereas that of normal Li₄Ti₅O₁₂ powders prepared by a sol–gel method can only achieve 100 mA h g^?1. This improved rate performance can be ascribed to small Li₄Ti₅O₁₂ nanocrystallites, a three‐dimensional mesoporous structure, and enhanced ionic conductivity.     

The role of Li2MO2 structures (M=metal ion) in the electrochemistry of (x)LiMn0.5Ni0.5O2·(1−x)Li2TiO3 electrodes for lithium-ion batteries

The electrochemical reactions of lithium with layered composite electrodes (x)LiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ were investigated at low voltages. The metal oxide 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ (x=0.95) which can also be represented in layered notation as Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂, can react with one equivalent of lithium during an initial discharge from 3.2 to 1.4 V vs. Li⁰. The electrochemical reaction, which corresponds to a theoretical capacity of 286 mAh/g, is hypothesized to form Li₂(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ that is isostructural with Li₂MnO₂ and Li₂NiO₂. Similar low-voltage electrochemical behavior is also observed with unsubstituted, standard LiMn_0.5Ni_0.5O₂ electrodes (x=1). In situ X-ray absorption spectroscopy (XAS) data of Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ electrodes indicate that the low-voltage (<1.8 V) reaction is associated primarily with the reduction of Mn⁴⁺ to Mn²⁺. Symmetric rocking-chair cells with the configuration Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂/Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ were tested. These electrodes provide a rechargeable capacity in excess of 300 mAh/g when charged and discharged over a 3.3 to −3.3 V range and show an insignificant capacity loss on the initial cycle. These findings have implications for combating the capacity-loss effects at graphite, metal–alloy, or intermetallic negative electrodes against lithium metal-oxide positive electrodes of conventional lithium-ion cells.     

Back Cover: Enhanced Electrochemical Performance of Ti‐Doping Li1.15Ni0.47Sb0.38O2 as Lithium‐excess Cathode for Lithium‐ion Batteries (Chin. J. Chem. 12/2017)

The back cover picture shows X‐ray near edge absorption spectroscopy has been applied to cathode materials for lithium‐ion batteries to explore its structure‐activity relationship. The result shows that in the Li‐rich cathode Li_1.15Ni_0.47Sb_0.38O₂, as a model system, Ti ions replaced the Li ions and then made an antistructure defect. It would change our understanding to the doped method for the cathode layer materials and benefit for designing other more powerful cathodes. In the picture, the road has been represented by the curve shape of the XANES of the as‐studied sample. The atomic arrangement around the Ti ion of the sample has been put into the tank position of the car. NSRL, National Synchrotron Radiation Laboratory, is the name of our laboratory. More details are discussed in the article by Chu et al. on page 1853–1860.

     

正极材料Li(Ni0.5Mn0.5)1-xMxO2 (M=Ti，Al；x=0，0.02)电化学行为的比较研究

0IntroductionMany efforts have been made to develop newmaterials as an alternative to LiCoO2due to the rela-tively high cost and toxicity of Co.Much attention hasbeen paid to layered structure cathode materials suchas LiMnO2and LiNiO2due to their lower co…     

LixNi0.5Co0.5O2的态密度计算及电化学性能研究

>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li_xNiO₂电化学性能的影响. 采用密度泛函DFT理论对Li_xNiO₂和Li_xNi_0.5Co_0.5O₂的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li_xNiO₂和Li_xNi_0.5Co_0.5O₂锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li_xNiO₂相比, Li_xNi_0.5Co_0.5O₂的电压平台相对较高(当0.25≤x≤0.5), 而且在Li^＋嵌/脱时, Li_xNi_0.5Co_0.5O₂的结构变化相对较小; Co离子的掺入, 减小了NiO₆八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO₆和CoO₆具有相互的稳定作用.     

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.     

Superstructure in the Metastable Intermediate‐Phase Li2/3FePO4 Accelerating the Lithium Battery Cathode Reaction

LiFePO₄ is an important cathode material for lithium‐ion batteries. Regardless of the biphasic reaction between the insulating end members, Li_xFePO₄, x≈0 and x≈1, optimization of the nanostructured architecture has substantially improved the power density of positive LiFePO₄ electrode. The charge transport that occurs in the interphase region across the biphasic boundary is the primary stage of solid‐state electrochemical reactions in which the Li concentrations and the valence state of Fe deviate significantly from the equilibrium end members. Complex interactions among Li ions and charges at the Fe sites have made understanding stability and transport properties of the intermediate domains difficult. Long‐range ordering at metastable intermediate eutectic composition of Li_2/3FePO₄ has now been discovered and its superstructure determined, which reflected predominant polaron crystallization at the Fe sites followed by Li⁺ redistribution to optimize the Li? Fe interactions.     

Properties and Structure of Spinel Li‐Mn‐O‐F Compounds for Cathode Materials of Secondary Lithium‐ion Battery

The spinel Li‐Mn‐O‐F compound cathode materials were synthesized by solid‐state reaction from calculated amounts LiOH‐H₂O, MnO₂(EMD) and LiF. The results of the electrochemical test demonstrated that these materials exhibited excellent electrochemical properties. It's initial capacity is ‐ 115 mAh.g¹ and reversible efficiency is about 100%. After 60 cycles, its capacity is still around 110 mAh.g¹ with nearly 100% reversible efficiency. The spinel Li‐Mn‐O‐F compound possibly has two structure models: interstitial model [Li]‐[Mn³⁺_xMn⁴⁺_2‐x]O₄F_δ, in which the fluorine is located on the interstice of crystal lattice, and substituted model [Li]‐[Mn³⁺_xMn⁴⁺_2‐x]O_4‐δF_δ, which the fluorine atom substituted the oxygen atom. The electrochemical result supports the interstitial model [Li][Mn³⁺_xMn⁴⁺_2‐x]O₄F_δ.     

A Perovskite Electrolyte That Is Stable in Moist Air for Lithium‐Ion Batteries

Solid‐oxide Li⁺ electrolytes of a rechargeable cell are generally sensitive to moisture in the air as H⁺ exchanges for the mobile Li⁺ of the electrolyte and forms insulating surface phases at the electrolyte interfaces and in the grain boundaries of a polycrystalline membrane. These surface phases dominate the total interfacial resistance of a conventional rechargeable cell with a solid–electrolyte separator. We report a new perovskite Li⁺ solid electrolyte, Li_0.38Sr_0.44Ta_0.7Hf_0.3O_2.95F_0.05, with a lithium‐ion conductivity of σ_Li=4.8×10^?4 S cm^?1 at 25 °C that does not react with water having 3≤pH≤14. The solid electrolyte with a thin Li⁺‐conducting polymer on its surface to prevent reduction of Ta⁵⁺ is wet by metallic lithium and provides low‐impedance dendrite‐free plating/stripping of a lithium anode. It is also stable upon contact with a composite polymer cathode. With this solid electrolyte, we demonstrate excellent cycling performance of an all‐solid‐state Li/LiFePO₄ cell, a Li‐S cell with a polymer‐gel cathode, and a supercapacitor.     

Electrochemically Generated γ‐LixV2O5 as Insertion Host for High‐Energy Li‐Ion Capacitors

In this study, we explored the feasibility of using electrochemically generated γ‐Li_xV₂O₅ as an insertion‐type anode in the lithium‐ion capacitor (LIC) with activated carbon (AC) as a cathode. Along with the native form of V₂O₅, their carbon composites are also used as the electrode material which is prepared by high‐energy ball milling. The electrochemical pre‐lithiation strategy is used to generate the desired γ‐phase of V₂O₅ (γ‐Li_xV₂O₅). Under the optimized mass loading conditions, the LICs are assembled with γ‐Li_xV₂O₅ as anode and AC as a cathode in the organic medium. Among the different LICs fabricated, AC/γ‐Li_xV₂O₅‐BM50 configuration delivered an energy density of 33.91 Wh kg^?1 @ 0.22 kW kg^?1 with excellent capacity retention characteristics. However, a dramatic increase in energy density (43.98 Wh kg^?1@0.28 kW kg^?1) is noted after the electrolyte modification with fluoroethylene carbonate. The high temperature performance of the assembled LIC is also studied and found that γ‐Li_xV₂O₅ phase can be used as a potential battery‐type component to construct high‐performance hybrid charge storage devices.     

An Ultra‐Long‐Life Lithium‐Rich Li1.2Mn0.6Ni0.2O2 Cathode by Three‐in‐One Surface Modification for Lithium‐Ion Batteries

Voltage decay and capacity fading are the main challenges for the commercialization of Li‐rich Mn‐based layered oxides (LLOs). Now, a three‐in‐one surface treatment is designed via the pyrolysis of urea to improve the voltage and capacity stability of Li_1.2Mn_0.6Ni_0.2O₂ (LMNO), by which oxygen vacancies, spinel phase integration, and N‐doped carbon nanolayers are synchronously built on the surface of LMNO microspheres. Oxygen vacancies and spinel phase integration suppress irreversible O₂ release and help lithium ion diffusion, while N‐doped carbon nanolayer mitigates the corrosion of electrolyte with excellent conductivity. The electrochemical performance of LMNO after the treatment improves significantly; the capacity retention rate after 500 cycles at 1 C is still as high as 89.9 % with a very small voltage fading rate of 1.09 mV cycle^?1. This three‐in‐one surface treatment strategy can suppress the voltage decay and capacity fading of LLOs.     

Nanoscale Surface Modification of Lithium‐Rich Layered‐Oxide Composite Cathodes for Suppressing Voltage Fade

Lithium‐rich layered oxides are promising cathode materials for lithium‐ion batteries and exhibit a high reversible capacity exceeding 250 mAh g⁻¹. However, voltage fade is the major problem that needs to be overcome before they can find practical applications. Here, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LLMO) oxides are subjected to nanoscale LiFePO₄ (LFP) surface modification. The resulting materials combine the advantages of both bulk doping and surface coating as the LLMO crystal structure is stabilized through cationic doping, and the LLMO cathode materials are protected from corrosion induced by organic electrolytes. An LLMO cathode modified with 5 wt % LFP (LLMO–LFP5) demonstrated suppressed voltage fade and a discharge capacity of 282.8 mAh g⁻¹ at 0.1 C with a capacity retention of 98.1 % after 120 cycles. Moreover, the nanoscale LFP layers incorporated into the LLMO surfaces can effectively maintain the lithium‐ion and charge transport channels, and the LLMO–LFP5 cathode demonstrated an excellent rate capacity.     

Sol-gel Synthesis and Electrochemical Performance of Li4-xMgxTi5-xZrxO12 Anode Material for Lithium-ion Batteries

The anode materials Li_4?xMg_xTi_5?xZr_xO₁₂ (x=0, 0.05, 0.1) were successfully synthesized by sol‐gel method using Ti(OC₄H₉)₄, CH₃COOLi·2H₂O, MgCl₂·6H₂O and Zr(NO₃)₃·6H₂O as raw materials. The crystalline structure, morphology and electrochemical properties of the as‐prepared materials were characterized by XRD, SEM, cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and charge‐discharge cycling tests. The results show that the lattice parameters of the Mg‐Zr doped samples are slightly larger than that of the pure Li₄Ti₅O₁₂, and Mg‐Zr doping does not change the basic Li₄Ti₅O₁₂ structure. The rate capability of Li_4?xMg_xTi_5?xZr_xO₁₂ (x=0.05, 0.1) electrodes is significantly improved due to the expansile Li⁺ diffusion channel and reduced charge transfer resistance. In this study, Li_3.95Mg_0.05Ti_4.95Zr_0.05O₁₂ represented a relatively good rate capability and cycling stability, after 400 cycles at 10 C, the discharge capacity retained as 134.74 mAh·g^?1 with capacity retention close to 100%. The excellent rate capability and good cycling performance make Li_3.95Mg_0.05Ti_4.95Zr_0.05O₁₂ a promising anode material in lithium‐ion batteries.     

Synergistic Dual‐Additive Electrolyte Enables Practical Lithium‐Metal Batteries

A rechargeable Li metal anode coupled with a high‐voltage cathode is a promising approach to high‐energy‐density batteries exceeding 300 Wh kg^?1. Reported here is an advanced dual‐additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate‐based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F‐ and B‐containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg^?1 at cell‐level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.     

Molybdenum Substitution for Improving the Charge Compensation and Activity of Li2MnO3

Lithium‐rich layer‐structured oxides xLi₂MnO₃? (1?x)LiMO₂ (0<x<1, M=Mn, Ni, Co, etc.) are interesting and potential cathode materials for high energy‐density lithium ion batteries. However, the characteristic charge compensation contributed by O^2? in Li₂MnO₃ leads to the evolution of oxygen during the initial Li⁺ ion extraction at high voltage and voltage fading in subsequent cycling, resulting in a safety hazard and poor cycling performance of the battery. Molybdenum substitution was performed in this work to provide another electron donor and to enhance the electrochemical activity of Li₂MnO₃‐based cathode materials. X‐ray diffraction and adsorption studies indicated that Mo⁵⁺ substitution expands the unit cell in the crystal lattice and weakens the Li?O and Mn?O bonds, as well as enhancing the activity of Li₂MnO₃ by lowering its delithiation potential and suppressing the release of oxygen. In addition, the chemical environment of O^2? ions in molybdenum‐substituted Li₂MnO₃ is more reversible than in the unsubstituted sample during cycling. Therefore molybdenum substitution is expected to improve the performances of the Li₂MnO₃‐based lithium‐rich cathode materials.     

Li3PO4‐Coated LiNi0.5Mn1.5O4: A Stable High‐Voltage Cathode Material for Lithium‐Ion Batteries

LiNi_0.5Mn_1.5O₄ is regarded as a promising cathode material to increase the energy density of lithium‐ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi_0.5Mn_1.5O₄ cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li₃PO₄ on LiNi_0.5Mn_1.5O₄ to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ is prepared by a solid‐state reaction and noncoated LiNi_0.5Mn_1.5O₄ is prepared by the same method as a control. The materials are fully characterized by XRD, FT‐IR, and high‐resolution TEM. TEM shows that the Li₃PO₄ layer (<6 nm) is successfully coated on the LiNi_0.5Mn_1.5O₄ primary particles. XRD and FT‐IR reveal that the synthesized Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ has a cubic spinel structure with a space group of Fd$\bar 3$ m, whereas noncoated LiNi_0.5Mn_1.5O₄ shows a cubic spinel structure with a space group of P4₃32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ shows dramatically enhanced cycling performance compared with noncoated LiNi_0.5Mn_1.5O₄.     

Electrospun V2O5 Nanostructures with Controllable Morphology as High‐Performance Cathode Materials for Lithium‐Ion Batteries

Porous V₂O₅ nanotubes, hierarchical V₂O₅ nanofibers, and single‐crystalline V₂O₅ nanobelts were controllably synthesized by using a simple electrospinning technique and subsequent annealing. The mechanism for the formation of these controllable structures was investigated. When tested as the cathode materials in lithium‐ion batteries (LIBs), the as‐formed V₂O₅ nanostructures exhibited a highly reversible capacity, excellent cycling performance, and good rate capacity. In particular, the porous V₂O₅ nanotubes provided short distances for Li⁺‐ion diffusion and large electrode–electrolyte contact areas for high Li⁺‐ion flux across the interface; Moreover, these nanotubes delivered a high power density of 40.2 kW kg^?1 whilst the energy density remained as high as 201 W h kg^?1, which, as one of the highest values measured on V₂O₅‐based cathode materials, could bridge the performance gap between batteries and supercapacitors. Moreover, to the best of our knowledge, this is the first preparation of single‐crystalline V₂O₅ nanobelts by using electrospinning techniques. Interestingly, the beneficial crystal orientation provided improved cycling stability for lithium intercalation. These results demonstrate that further improvement or optimization of electrochemical performance in transition‐metal‐oxide‐based electrode materials could be realized by the design of 1D nanostructures with unique morphologies.     

The Stabilization Effect of CO2 in Lithium–Oxygen/CO2 Batteries

The lithium (Li)–air battery has an ultrahigh theoretical specific energy, however, even in pure oxygen (O₂), the vulnerability of conventional organic electrolytes and carbon cathodes towards reaction intermediates, especially O₂^?, and corrosive oxidation and crack/pulverization of Li metal anode lead to poor cycling stability of the Li‐air battery. Even worse, the water and/or CO₂ in air bring parasitic reactions and safety issues. Therefore, applying such systems in open‐air environment is challenging. Herein, contrary to previous assertions, we have found that CO₂ can improve the stability of both anode and electrolyte, and a high‐performance rechargeable Li–O₂/CO₂ battery is developed. The CO₂ not only facilitates the in situ formation of a passivated protective Li₂CO₃ film on the Li anode, but also restrains side reactions involving electrolyte and cathode by capturing O₂^?. Moreover, the Pd/CNT catalyst in the cathode can extend the battery lifespan by effectively tuning the product morphology and catalyzing the decomposition of Li₂CO₃. The Li–O₂/CO₂ battery achieves a full discharge capacity of 6628 mAh g^?1 and a long life of 715 cycles, which is even better than those of pure Li–O₂ batteries.