Structural degradation mechanism of oxysulfide spinel LiAl 0.24Mn1.76O3.98S0.02 cathode materials on high temperature cycling

Structural degradation of oxysulfide spinel, LiAl_0.24Mn_1.76O_3.98S_0.02 electrode in the 4 V region (4.3–3.0 V) cycled at high temperature has been investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The capacity loss during cycling is noticeably increased in the cell operation temperature from 50°C to 80°C. HRTEM study shows that the rock salt phase Li₂MnO₃ has been detected at the particle surface of discharged spinel electrode cycled at 80°C. The capacity loss of the spinel electrode at high temperature is ascribed to the MnO dissolution from the formed Li₂Mn₂O₄ at the particle surface.     

Enhancing the electrochemical performance of Li1.2Ni0.2Mn0.6O2 by surface modification with nickel–manganese composite oxide

Li-rich layered Li_1.2Ni_0.2Mn_0.6O₂ has been surface modified by nickel–manganese composite oxide (Ni_0.5Mn_1.5O _x ) to serve as a novel cathode material with novel layered spinel structure for lithium-ion battery. The as-prepared Li_1.2Ni_0.2Mn_0.6O₂ before and after surface modification by Ni_0.5Mn_1.5O _x as well as simply blended Li_1.2Ni_0.2Mn_0.6O₂ with spinel LiNi_0.5Mn_1.5O₄, have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electronic microscopy, and differential scanning calorimetry. Electrochemical studies indicate that the Ni_0.5Mn_1.5O _x surface modified Li_1.2Ni_0.2Mn_0.6O₂ with peculiar layered spinel character dramatically represented increased discharge capacity, improved cycling stability as well as excellent rate capability at high-voltage even up to 5.0 V.     

Preparation and electrochemical characterization of a polymer Li1.03Mn1.97O4/pEDOT composite electrode

The development and characterization of a polymeric composite based on non-stoichiometric Li_1.03Mn_1.97O₄ spinel operating at 4 V and poly(3,4-ethylenedioxy)thiophene (pEDOT) are reported. In this composite the pEDOT substitutes the carbon usually mixed with the inorganic oxide-based electrodes to improve their electronic conductivity; the pEDOT thus functions as an electronic conductor and is electroactive in the same potential range of LiMn₂O₄. Electrochemical data for pure pEDOT and for composites of pEDOT/carbon, conventional Li_1.03Mn_1.97O₄/carbon and polymer Li_1.03Mn_1.97O₄/pEDOT are reported and discussed.     

Synthesis and electrochemical characteristics of oxysulfide spinel material for lithium secondary batteries

Oxysulfide spinel LiMn₂O_3.98S_0.02 powders with monodispersed, and highly homogeneous particles were synthesized by a sol-gel method using an aqueous solution of metal acetates and sulfide containing glycolic acid as a chelating agent. The oxysulfide spinel, LiMn₂O_3.98S_0.02 electrode initially delivers 80 mAh g⁻¹, steadily increases during cycling, and reaches 99 mAh g⁻¹ at the 20th cycle. The substitution of a small amount S for O in LiMn₂O₄ spinel helps to maintain structural integrity during cycling, which then overcomes the Jahn–Teller distortion in the spinel Mn phase in the 3 V region.     

锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2的酸浸改性研究

为提高锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2的首次充放电效率,对固相法合成的该材料进行了酸浸的改性研究。通过X射线衍射(XRD)、扫描电子显微镜(SEM)对所得样品的结构、形貌进行了表征。结果表明,Li[Li0.2Ni0.2Mn0.6]O2经过酸处理后,首次放电效率得到了较大的提高,但是放电中值电压明显下降。其中,0.5 mol.L-1的硝酸浸泡5 h的效果最佳,首次放电效率达到了86.7%,同时放电容量达到最大值的循环次数大大减少。酸浸改性的原因被归结于材料表面出现了富锂尖晶石结构Li4Mn5O12相。     

Synthesis of Li[Li0.2Ni0.2Mn0.6]O2 by radiated polymer gel method and impact of deficient Li on its structure and electrochemical properties

Layered Li[Li_0.16Ni_0.21Mn_0.63]O₂ and Li[Li_0.2Ni_0.2Mn_0.6]O₂ compounds were successfully synthesized by radiated polymer gel (RPG) method. The effect of deficient Li on the structure and electrochemical performance was investigated by means of X-ray diffraction, X-ray absorption near-edge spectroscopy and electrochemical cell cycling. The reduced Ni valence in Li[Li_0.16Ni_0.21Mn_0.63]O₂ leads to a higher capacity owing to faster Li⁺ chemical diffusivity relative to the baseline composition Li[Li_0.2Ni_0.2Mn_0.6]O₂. Cyclic voltammograms (CV) and a simultaneous direct current (DC) resistance measurement were also performed on Li/Li[Li_0.16Ni_0.21Mn_0.63]O₂ and Li/Li[Li_0.2Ni_0.2Mn_0.6]O₂ cells. Li[Li_0.16Ni_0.21Mn_0.63]O₂ shows better electrochemical performance with a reversible capacity of 158 mA hg⁻¹ at 1C rate at 20 °C.     

Effect of mono- (Cr) and bication (Cr, V) substitution on LiMn2O4 spinel cathodes

A study on the structural and electrochemical properties of LiCr_0.2Mn_1.8O₄ and LiV_0.2Cr_0.2Mn_1.6O₄ cathodes has been made with a view to understand the effect of mono- (Cr) and bication (Cr and V) substitution on LiMn₂O₄ spinel individually. Citric acid assisted modified sol–gel method has been followed to synthesize a series of LiMn₂O₄, LiCr_0.2Mn_1.8O₄, and LiV_0.2Cr_0.2Mn_1.6O₄ cathodes, and the corresponding lattice structure, surface morphology, and site occupancy of lithium in the spinel matrix are acknowledged using X-ray diffraction, scanning electron microscopy, and magic angle spinning ⁷Li nuclear magnetic resonance results. The site occupancy of Cr³⁺ in the 16d octahedral and that of V⁵⁺ in the 16d octahedral and 8a tetrahedral positions are understood. Electrochemical cycling studies of LiCr_0.2Mn_1.8O₄ cathode demonstrate an enhanced structural stability and better capacity retention (94%) resulting from the Cr³⁺ dopant-induced co-valency of Li-O-Mn bond. On the other hand, simultaneous substitution of Cr and V in LiV_0.2Cr_0.2Mn_1.6O₄ has failed to improve the electrochemical properties of native LiMn₂O₄ spinel cathode, mainly due to vanadium-driven cation mixing and the reduced lithium diffusion kinetics. Among the candidates chosen for the study, LiCr_0.2Mn_1.8O₄ qualifies itself as a better cathode for rechargeable lithium battery applications.     

High capacity lithium-manganese-nickel-oxide composite cathodes with low irreversible capacity loss and good cycle life for lithium ion batteries

We report a method to eliminate the irreversible capacity of 0.4Li_2MnO_3·0.6LiNi_(0.5)Mn_(0.5)O_2(Li_(1.17)Ni_(0.25)Mn_(0.583)O_2) by decreasing lithium content to yield integrated layered-spinel structures.XRD patterns,High-resolution TEM image and electrochemical cycling of the materials in lithium cells revealed features consistent with the presence of spinel phase within the materials.When discharged to about 2.8 V,the spinel phase of LiM_2O_4(M=Ni,Mn) can transform to rock-salt phase of Li_2M_2O_4(M=Ni,Mn) during which the tetravalent manganese ions are reduced to an oxidation state of 3.0.So the spinel phase can act as a host to insert back the extracted lithium ions(from the layered matrix) that could not embed back into the layered lattice to eliminate the irreversible capacity loss and increase the discharge capacity.Their electrochemical properties at room temperature showed a high capacity(about 275 mAh g~(-1) at 0.1 C) and exhibited good cycling performance.     

锂离子电池负极材料Li_(4-x)K_xTi_5O_(12)结构和电化学性能

采用固相反应的方法制备了尖晶石型Li4Ti5O12和K掺杂Li4-xKxTi5O12(x=0.02,0.04,0.06)。通过XRD、SEM、BET等对制备材料进行了分析。结果表明,K掺杂没有影响立方尖晶石型Li4Ti5O12的合成,同时也没有改变Li4Ti5O12的电化学反应过程。K掺杂Li4-xKxTi5O12具有比Li4Ti5O12小的颗粒粒径和比Li4Ti5O12大的比表面积、孔容积。适量的K掺杂能够明显改善Li4Ti5O12的电化学性能,尤其是倍率性能,但是过多的K掺杂却不利于材料电化学性能的提高。研究表明,Li3.96K0.04Ti5O12体现了相对较好的倍率性能和循环稳定性。0.5C下,首次放电比容量为161mAh·g-1,3.0和5.0C下,容量保持分别为138和121mAh·g-1。3.0C下,200次循环后容量保持为137mAh·g-1。     

Stabilizing Cobalt-free Li-rich Layered Oxide Cathodes through Oxygen Lattice Regulation by Two-phase Ru Doping

The application of Li-rich layered oxides is hindered by their dramatic capacity and voltage decay on cycling. This work comprehensively studies the mechanistic behaviour of cobalt-free Li_1.2Ni_0.2Mn_0.6O₂ and demonstrates the positive impact of two-phase Ru doping. A mechanistic transition from the monoclinic to the hexagonal behaviour is found for the structural evolution of Li_1.2Ni_0.2Mn_0.6O_2, and the improvement mechanism of Ru doping is understood using the combination of in operando and post-mortem synchrotron analyses. The two-phase Ru doping improves the structural reversibility in the first cycle and restrains structural degradation during cycling by stabilizing oxygen (O²⁻) redox and reducing Mn reduction, thus enabling high structural stability, an extraordinarily stable voltage (decay rate <0.45 mV per cycle), and a high capacity-retention rate during long-term cycling. The understanding of the structure-function relationship of Li_1.2Ni_0.2Mn_0.6O₂ sheds light on the selective doping strategy and rational materials design for better-performance Li-rich layered oxides.     

Improvement of electrochemical performance for Li-rich spherical Li1.3[Ni0.35Mn0.65]O2+x modified by Al2O3

The Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x microspheres are firstly prepared and subsequently transferred into the Al₂O₃-coated Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x microspheres by a simple deposition method. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results reveal that the Al₂O₃-coated Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x sample has a typical α-NaFeO₂ layered structure with the existence of Li₂MnO₃-type integrated component, and the Al₂O₃ layer is uniformly coated on the surface of the spherical Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x particles with a thickness of about 4 nm. Importantly, the Al₂O₃-coated Li-rich sample exhibits obviously improved electrochemical performance compared with the pristine one, especially the 2 wt.% Al₂O₃-coated sample shows the best electrochemical properties, which delivers an initial discharge capacity of 228 mAh g^?1 at a rate of 0.1 C in the voltage of 2.0–4.6 V, and the first coulombic efficiency is up to 90 %. Furthermore, the 2 wt.% Al₂O₃-coated sample represents excellent cycling stability with capacity retention of 90.9 % at 0.33 C after 100 cycles, much higher than that of the pristine one (62.2 %). Particularly, herein, the typical inferior rate capability of Li-rich layered cathode is apparently improved, and the 2 wt.% Al₂O₃-coated sample also shows a high rate capability, which can deliver a capacity of 101 mAh g^?1 even at 10 C. Besides, the thin Al₂O₃ layer can reduce the charge transfer resistance and stabilize the surface structure of active material during cycling, which is responsible for the improvement of electrochemical performance of the Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x .     

Chemical and structural transformations in manganese aluminum spinel of the composition Mn1.5Al1.5O4 during heating and cooling in air

Single phase cubic spinel of the composition Mn_1.5Al_1.5O₄ is synthesized. Its crystal structure refinement shows that 0.4Mn+0.6Al are in the octahedral sites and 0.7Mn+0.3Al are in the tetrahedral sites. High temperature X-ray diffraction is used to analyze Mn_1.5Al_1.5O₄ behavior during heating and cooling in air. In a temperature range of 600°C to 700°C, initial spinel splits into layers, and the sample represents a twophase system: cubic spinel Mn_0.4Al_2.4O₄ and a phase based on β-Mn₃O₄. Above 900°C the sample again turns into single phase cubic spinel. The role of oxidizing processes in the decomposition of Mn_1.5Al_1.5O₄ caused by oxygenation and partial oxidation of Mn²⁺ to Mn³⁺ is shown. A scheme of structural transformations of manganese aluminum spinel during heating from room temperature and cooling from 950°C is proposed.     

Eliminating Voltage Decay of Lithium‐Rich Li1.14Mn0.54Ni0.14Co0.14O2 Cathodes by Controlling the Electrochemical Process

A lithium‐rich cathode material Li_1.14Mn_0.54Ni_0.14Co_0.14O₂ (LNMCO) is prepared by a co‐precipitation method. The issue of voltage decay in long‐term cycling is largely eliminated by control of the charge–discharge voltage range. The LNMCO material exhibits 9.8 % decay in discharge voltage over 200 cycles between 2.0–4.6 V, during which the working voltage decays significantly, from 3.57 V to 3.22 V. The decay was decelerated by a factor of six by using a voltage window of 2.0–4.4 V, from 3.53 V to 3.47 V. IR and Raman spectra reveal that the transformation of layered structure to spinel is significantly retarded under 2.0–4.4 V cycling conditions. Transmission electron microscopy (TEM) was also applied for examining phase change in an individual particle during cycling, showing that the spinel phase occurs both at 2.0–4.6 V and at 2.0–4.4 V, but is not dominant in the latter. Normalization of Li can remove the additional impact on the voltage decay which is brought by different amounts of Li intercalation. The mechanism of no voltage decay at 2.0–4.4 V cycling is raised and electrochemical impedance spectrum data also support the hypothesis.     

Synthesis of single-crystal magnesium-doped spinel lithium manganate and its applications for lithium-ion batteries

Single-crystal magnesium-doped spinel lithium manganate cathode materials are prepared by the hydrothermal method followed by the heat treatment. XRD patterns reveal that Mg²⁺ions have already diffused into the Li_1.088Mn_1.912O₄ crystal structure and not affect the Fd3m space group. SEM images demonstrate that the magnesium-doped spinel lithium manganates show uniform polyhedral single crystals with 2–4 μm. Electrochemical performance demonstrates that the optimized composition of Li_1.088Mg_0.070Mn_1.842O₄ electrode exhibits the best electrochemical properties. It delivers 92.0 mAh g^?1 at 8C rates and corresponds to 90.8% capacity retention (vs. 1C), far higher than those of the pristine electrode (70.4 mAh g^?1 and 69.2%). In addition, the Li_1.088Mg_0.070Mn_1.842O₄ electrode also shows 95.5% capacity retention after 100 cycles at 1C, while the pristine electrode only shows 91.0% capacity retention. The excellent electrochemical performances of Li_1.088Mg_0.070Mn_1.842O₄ electrode are ascribed to the suppressed polarization, more stable crystal structure, and better kinetic characteristics.     

Lithium–manganese–nickel-oxide electrodes with integrated layered–spinel structures for lithium batteries

A series of lithium–manganese–nickel-oxide compositions that can be represented in three-component notation, xLi[Mn_1.5Ni_0.5]O₄ · (1 − x){Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂}, in which a spinel component, Li[Mn_1.5Ni_0.5]O₄, and two layered components, Li₂MnO₃ and Li(Mn_0.5Ni_0.5)O₂, are structurally integrated in a highly complex manner, have been evaluated as electrodes in lithium cells for x = 1, 0.75, 0.50, 0.25 and 0. In this series of compounds, which is defined by the Li[Mn_1.5Ni_0.5]O₄–{Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂} tie-line in the Li[Mn_1.5Ni_0.5]O₄–Li₂MnO₃–Li(Mn_0.5Ni_0.5)O₂ phase diagram, the Mn:Ni ratio in the spinel and the combined layered Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ components is always 3:1. Powder X-ray diffraction patterns of the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the spinel Li[Mn_1.5Ni_0.5]O₄ (x = 1) and for ‘composite’ Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ layered electrode structures (x = 0). Electrodes with intermediate values of x exhibit both spinel and layered character and yield extremely high capacities, reaching more than 250 mA h/g with good cycling stability between 2.0 V and 4.95 V vs. Li° at a current rate of 0.1 mA/cm².     

Solid-state electrochemical lithium cells with oxide electrodes and composite solid electrolyte

The LiClO₄-Al₂O₃ composite solid electrolyte and solid solutions LiFe _x Mn_2?x O₄ and Li₅Ti₄O₁₂ compositions are synthesized and their physicochemical properties are studied using the x-ray diffraction and electrical measurements. Based on composition 0.5LiClO₄-0.5Al₂O₃, whose conductivity is the highest, first experiments on the elaboration of model electrochemical solid-electrolyte lithium cells with LiMn₂O₄, LiFeMnO₄, LiFe_0.8Mn_0.2O₄, and Li₅Ti₄O₁₂ oxide spinel electrodes are performed.     

High-temperature X-ray study of the formation and delamination of manganese-alumina spinel Mn<Subscript>1.5</Subscript>Al<Subscript>1.5</Subscript>O<Subscript>4</Subscript>

The behavior of the manganese-alumina system with Mn:Al = 1:1 on heating in air and vacuum was studied. The starting samples were mixtures of β-Mn₃O₄, α-Mn₂O₃, and γ-Al₂O₃. On heating to 950°C in air, the samples were partially oxidized into α-Mn₂O₃, and corundum α-Al₂O₃ formed along with mixed manganese-alumina cubic spinel, whose composition was close to Mn₂AlO₄. In vacuum at 1200°C, the starting sample with a ratio of Mn:Al = 1:1 transformed into the manganese-alumina spinel Mn_1.5Al_1.5O₄, which retained its cubic structure after slow cooling in vacuum. When cooled in air, this solid solution delaminated, and a nanocrystalline Mn_2.8Al_0.2O₄ phase formed, whose structure was β-Mn₃O₄ type tetragonal spinel.     

The electrochemical performance of sodium-ion-modified spinel LiMn2O4 used for lithium-ion batteries

The spinel LiMn₂O₄ cathode material has been considered as one of the most potential cathode active materials for rechargeable lithium ion batteries. The sodium-doped LiMn₂O₄ is synthesized by solid-state reaction. The X-ray diffraction analysis reveals that the Li_1?x Na _x Mn₂O₄ (0?≤?x?≤?0.01) exhibits a single phase with cubic spinel structure. The particles of the doped samples exhibit better crystallinity and uniform distribution. The diffusion coefficient of the Li_0.99Na_0.01Mn₂O₄ sample is 2.45?×?10^?10 cm^?2 s^?1 and 3.74?×?10^?10 cm^?2 s^?1, which is much higher than that of the undoped spinel LiMn₂O₄ sample, indicating the Na⁺-ion doping is favorable to lithium ion migration in the spinel structure. The galvanostatic charge–discharge results show that the Na⁺-ion doping could improve cycling performance and rate capability, which is mainly due to the higher ion diffusion coefficient and more stable spinel structure.     

LiNi0.05Mn1.95O4的合成及对Li+的离子交换动力学

用溶胶-凝胶法合成出尖晶石结构的LiNi0.05Mn1.95O4,用0.5 mol·L-1过硫酸铵对其进行改型,制得锂离子筛LiNiMn-H.LiNiMn-H对Li+的饱和交换容量达5.2 mmol·g-1.用缩核模型(Shrinking-Core Model)处理该离子交换的反应动力学数据得到LiNiMn-H吸附Li+时离子交换反应的控制步骤是颗粒扩散控制(PDC),同时得到了该实验条件下锂离子筛LiNiMn-H吸附Li+的动力学方程和颗粒扩散系数De.     

Variation of the composition and properties of lithium manganese oxide spinel in lithiation-delithiation cycles

The behavior of the variable-composition spinel Li_{1 + x} Mn_{2 ? x} O₄ is examined in repeated cycles consisting of lithiation in 0.2 M LiOH and delithiation in 0.3 M HNO₃. For 0 < x < 0.33, delithiation is accompanied by the redox reaction 2Mn³⁺ → Mn⁴⁺ + Mn²⁺ and Li⁺ ? H⁺ ion exchange. The spinel undergoes partial conversion into λ-□MnO₂. Vacancies (□) build up at the 8a sites of the spinel structure. Mn²⁺ ions pass into the solution, and, accordingly, the spinel dissolves. Lithiation is accompanied by the redox reaction 4Mn⁴⁺ → 3Mn³⁺ + Mn⁷⁺ and ion exchange, and the proportion of vacancies □ at the 8a sites of the spinel structure decreases. The spinel undergoes partial dissolution because of Mn²⁺ and MnO _? ⁴ ions passing into the solution. The Li⁺ selectivity of the spinel is the property of the crystallite core. The crystallite surface is capable of sorbing Na⁺ ions.