Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel material by fluorine substitution

LiNi_0.5Mn_1.5O_4−xF_x (0 ≤ x ≤0.1) cathodes, synthesized by ultrasonic spray pyrolysis at 900 °C, exhibit superior structural and electrochemical properties. The samples are characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and electrochemical measurements. During Li⁺ extraction, LiNi_0.5Mn_1.5O_4−xF_x has a smaller lattice variation and area-specific impedance than LiNi_0.5Mn_1.5O₄. This enhances the rate capability, especially at high C-rates. LiNi_0.5Mn_1.5O_4−xF_x also exhibits better resistance than LiNi_0.5Mn_1.5O₄ to attack by HF.     

The cycle life investigation for spinel LiNi0.5Mn1.5O4 full cells

分别以石墨和钛酸锂为负极活性物质,制备了尖晶石镍锰酸锂的32131型圆柱锂离子电池.石墨负极电池和钛酸锂负极电池容量分别为7.5 A·h和5.5 A·h,质量能量密度分别达到152 W·h/kg和81 W·h/kg.常温充放电循环测试结果表明,石墨和钛酸锂两种负极体系电池循环寿命将分别达到400次和1000次,这种循环寿命的差别主要体现在负极上,即正极材料中溶解的Mn在石墨负极表面沉积并持续催化SEI膜生成,减少了电池中可使用的活性Li⁺,进而导致电池寿命快速衰减;相比而言,钛酸锂负极表面不存在明显SEI,同时正极过量设计电池也使得钛酸锂体系电池的镍锰酸锂与电解液间的界面副反应低于石墨体系的负极过量设计电池.     

Preparation,electrochemical performance and phase transition of high voltage LiNi0.5Mn1.5O4 cathode material

尖晶石LiNi_0.5Mn_1.5O₄因其可在4.7 V高电位下工作并有良好的循环特性,已成为最具潜力的高能量密度锂离子电池正极材料。本文首先采用喷雾干燥辅助烧结法制备了LiNi_0.5Mn_1.5O₄正极材料,考察了热处理条件对材料结构与性能的影响。用XRD、SEM和FT-IR等技术对所制备的LiNi_0.5Mn_1.5O₄材料的结构和表面形貌进行表征,利用原位XRD技术研究了LiNi_0.5Mn_1.5O₄正极材料在充放电过程中结构相变规律。结果表明,所制备的LiNi_0.5Mn_1.5O₄材料均具有Fd-3m空间群的立方相尖晶石型结构,并具有优异的电化学性能,其0.1 C时首次放电容量为132 mA·h/g,首轮库仑效率93.48%,高倍率下该材料的电化学性能优越。原位XRD测量结果分析表明,尖晶石型LiNi_0.5Mn_1.5O₄材料在充电过程中存在4个显著的相变过程,在嵌脱锂过程中,从四面体相向立方相结构相变过程是可逆的。     

Exploration of high capacity LiNi0.5Mn1.5O4 synthesized by solid-state reaction

LiNi_0.5Mn_1.5O₄ was prepared by an improved solid-state reaction at high heating and cooling rates, the mixed precursors were initially heated up to 900 °C, then directly cooled down to 600 °C and heated for 24 h in air. X-ray diffraction (XRD) pattern shows that LiNi_0.5Mn_1.5O₄ has cubic spinel structure; scanning electron microscopic (SEM) image shows that the particle size is about 0.2 μm together with homogenous distribution. Electrochemical measurements show that LiNi_0.5Mn_1.5O₄ powders delivered up to 143 mAh g⁻¹ with superior cycling performance at the rate of 5/7C.     

Effect of sulfur and nickel doping on morphology and electrochemical performance of LiNi0.5Mn1.5O4−xSx spinel material in 3-V region

The effect of nickel and sulfur substitution for manganese and oxygen on the structure and electrochemical properties of the LiNi_0.5Mn_1.5O_4−xS_x is examined. The LiNi_0.5Mn_1.5O_4−xS_x (x = 0 and 0.05) compounds are successfully synthesized at 500 and 800 °C by co-precipitation using the metal carbonate (Ni_0.5Mn_1.5)CO₃ as a precursor. The resulting powder with sulfur doping exhibits different morphology from a Ni-only doped spinel in terms of particle size and surface texture. The LiNi_0.5Mn_1.5O_4−xS_x (x = 0 and 0.05) powders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge–discharge cycling. The nickel- and sulfur-doped spinel displays excellent capacity retention and rate capability in the 3-V region, compared with Ni-only doped spinel material.     

Influence of magnetic properties on electrochemical activity of LiNi0.5Fe0.5O2

LiNi_0.5Fe_0.5O₂ is prepared by a sol–gel method and the sample is heat-treated to various temperatures to characterize its physico-chemical properties. Calcination of the precursor at 673 K produces powders of tetragonal and hexagonal phases. Subsequent heat treatment at 873, 1073 and 1273 K results in a pure hexagonal phase. Vibrating sample magnetometer (VSM) studies show that the tetragonal phase is magnetically stronger than the hexogonal phase. Room-temperature Mössbauer studies reveal magnetic ordering for the tetragonal phase and the paramagnetic nature of the hexagonal phase. The hexagonal phase is magnetically ordered at 77 K. By comparing the value of the hyperfine field with the bulk magnetization value at 77 K obtained from VSM, it is concluded that the magnetic ordering cannot be ferromagnetic but should be antiferromagnetic.     

LiNi0.5Mn1.5O4 thick-film electrodes prepared by electrophoretic deposition for use in high voltage lithium-ion batteries

Highly homogeneous coatings several microns in thickness were prepared by electrophoretic deposition (EPD) from suspensions of a well-crystallized spinel of nominal composition LiNi_0.5Mn_1.5O₄ mixed with 10% carbon black. The best dispersing conditions were found to be those provided by acetone containing citric acid and polyethyleneimine as dispersing agents; this combination resulted in increased mobility of particles and improved adherence to the substrate. These experimental conditions favored deposition of the smallest particles, thereby increasing coating uniformity. The as-prepared coatings were used as electrodes in lithium cells and found to provide virtually no electrochemical response owing to the lack of interparticle connectivity. This problem was easily overcome by compressing the coatings. Thus, coatings compressed at 517 MPa resulted in cell performance on a par with that of the cell made from the bulk spinel. Moreover, their small particle size facilitates lithium-ion diffusion and the deposits exhibit good rate capabilities and coulombic efficiencies.     

Electrochemical performance behavior of combustion-synthesized LiNi0.5Mn0.5O2 lithium-intercalation cathodes

LiNiO₂, partially substituted with manganese in the form of a LiNi_0.5Mn_0.5O₂ compound, has been synthesized by a gelatin assisted combustion method [GAC] method. Highly crystalline LiNi_0.5Mn_0.5O₂ powders with R3m symmetry have been obtained at an optimum temperature of 850 °C, as confirmed by PXRD studies. The presence of cathodic and anodic CV peaks exhibited by the LiNi_0.5Mn_0.5O₂ cathode at 4.4 and 4.3 V revealed the existence of Ni and Mn in their 2+ and 4+ oxidation states, respectively. The synthesized LiNi_0.5Mn_0.5O₂ cathode has been subjected to systematic electrochemical performance evaluation, via capacity tapping at different cut-off voltage limits (3.0–4.2, 3.0–4.4 and 3.0–4.6 V) and the possible extraction of deliverable capacity under different current drains (0.1C, 0.5C, 0.75C and 1C rates). The LiNi_0.5Mn_0.5O₂ cathode exhibited a maximum discharge capacity of 174 mAh g⁻¹ at the 0.1C rate between 3.0 and 4.6 V. However, a slightly decreased capacity of 138 mAh g⁻¹ has been obtained in the 3.0–4.4 V range, when discharged at the 1C rate. On the other hand, extended cycling at the 0.1C rate encountered an acceptable capacity fade in the 3.0–4.4 V range (<10%) for up to 50 cycles.     

All-solid-state lithium secondary batteries using a layer-structured LiNi0.5Mn0.5O2 cathode material

All-solid-state cells of In/LiNi_0.5Mn_0.5O₂ using a superionic oxysulfide glass with high conductivity at room temperature of 10⁻³ S cm⁻¹ as a solid electrolyte were fabricated and the cell performance was investigated. Although a large irreversible capacity was observed at the 1st cycle, the solid-state cells worked as lithium secondary batteries and exhibited excellent cycling performance after the 2nd cycle; the cells kept charge–discharge capacities around 70 mAh g⁻¹ and its efficiency was almost 100%. This is the first case to confirm that all-solid-state cells using manganese-based layer-structured cathode materials work as lithium secondary batteries.     

Improvement of electrochemical and structural properties of LiMn2O4 spinel based electrode materials for Li-ion batteries

Spinel LiMn₂O₄ and LiM_0.02Mn_1.98O₄ (where M is Zn, Co, Ni and In) were produced via facile sol–gel method and Cu/LiMn₂O₄, Cu/LiM_0.02Mn_1.98O₄, Ag/LiMn₂O₄ and Ag/LiM_0.02Mn_1.98O₄ binary composite electrode materials were produced via electroless coating techniques as a positive electrode material for Li-ion batteries. The phase composition, morphology and electrochemical properties of the synthesized materials were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), cyclic voltammometry (CV), galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). The synthesized cathode active materials are characterized as single phase spinel LiMn₂O₄ with degree of crystallization and uniform particle size distribution. Best results were obtained with electrodes substituted with In and an initial discharge capacity of 134 mAhg⁻¹ after 50 cycles. The improvement in the cycling performance may be attributed to stabilization of spinel structure by smaller lattice constant when manganese ion was partially substituted with In³⁺ ions. EIS analysis also confirms that the obvious improvement in Ag coating is mainly attributed to the accelerated phase transformation from layered phase to spinel phase and highly stable electrolyte/electrode interface due to the suppression of electrolyte decomposition.     

Studies of cycling behavior,ageing, and interfacial reactions of LiNi0.5Mn1.5O4 and carbon electrodes for lithium-ion 5-V cells

The cycling and storage behavior of LiNi_0.5Mn_1.5O₄ and MCMB electrodes for 5-V Li-ion batteries was investigated at elevated temperatures using a variety of electrochemical (CV, EIS) and spectroscopic (XPS, micro-Raman) tools. It was established that LiNi_0.5Mn_1.5O₄ electrodes could be cycled highly reversibly, demonstrating sufficient capacity retention at 60 °C by a constant current/constant voltage mode in DMC–EC/1.5 M LiPF₆ solutions. By studying the influence of temperature on the impedance of LiNi_0.5Mn_1.5O₄ electrodes, we conclude that when the initial electrode's surface chemistry is developed at a high temperature (60 °C) it becomes nearly invariant, and hence, their impedance remains steady upon cycling and storage. Prolonged storage of these electrodes at 60 °C may result in local Mn and Ni dissolution and transformation of the active material to λ-MnO₂. We have found that the surface chemistry of aged LiNi_0.5Mn_1.5O₄ electrodes (free of carbon black and PVdF) involves the formation of LiF, C–F and P–F_x species. Storage of MCMB electrodes in LiPF₆ containing solutions at open circuit conditions (before their first lithiation) leads to significant morphological changes and the formation of lithium fluoride on the electrode surface, as determined by the XRD studies. LiF is probably a product of a catalytic thermal decomposition of LiPF₆. These initial changes further influence the impedance and kinetics of the lithiated electrodes.     

Investigation of Ti-substitution effects on structural and electrochemical properties of Na0.67Mn0.5Fe0.5O2 battery cells

Ti-substituted Na_0.67Mn_0.5Fe_0.5O₂ powders were fabricated by quenching at high temperatures, and the structural properties were investigated by Fourier transform infrared (FTIR), Scanning Electron Microscope (SEM), X-ray powder diffraction (XRD), and X-ray absorption spectroscopy (XAS) measurements. According to XRD analysis, it was not observed any impurity phases and it was found that the lattice constants of the powders were slightly increased by Ti content. The change in the valence state of both Mn and Fe ions was investigated by X-ray absorption near edge structure (XANES), and it was found that Ti-substitution caused a decrease in the valance state of Fe in Na_0.67Mn_0.5Fe_0.5O₂. Fourier transform (FT) of XANES showed that the local structure around the metal ions changed with the addition of Ti ions. The cycling voltammetry (CV) graphs of Ti-substituted cells were almost the same as the pure sample, which may not change the cycling mechanism in the cells. According to galvanostatic cycling measurements at room temperature, the best performance was obtained with Ti-substitution of 0.06 to 0.09 in the structure. The effect of environmental temperature in the battery cells was investigated at 10°C to 50°C, and it was found that the battery performance depends on the environmental temperatures.     

Improved electrochemical properties of a coin cell using LiMn1.5Ni0.5O4 as cathode in the 5 V range

Phase pure LiMn_1.5Ni_0.5O₄ powders were synthesized by a chemical synthesis route and were subsequently characterized as cathode materials in a Li-ion coin cell comprising a Li anode and lithium hexafluorophosphate (LiPF₆), dissolved in dimethyl carbonate (DMC) + ethylene carbonate (EC) [1:1, v/v ratio] as electrolyte. The spinel structure and phase purity of the powders were characterized using X-ray diffraction and micro-Raman spectroscopy. The presence of both oxidation and reduction peaks in the cyclic voltammogram revealed Li⁺ extraction and insertion from the spinel structure. The charge–discharge characteristics of the coin cell were performed in the 3.0–4.8 V range. An initial discharge capacity of ∼140 mAh g⁻¹ was obtained with 94% initial discharge capacity retention after 50 repeated cycles. The microstructures and compositions of the cathode before and after electrochemistry were investigated using scanning electron microscopy and energy-dispersive analysis by X-ray analysis, respectively. Using X-ray diffraction, Raman spectroscopy and electrochemical analysis, we correlated the structural stability and the electrochemical performance of this cathode.     

Preparation and electrochemical properties of Zn-doped LiNi0.8Co0.2O2

Zn-doped LiZn_yNi_0.8−yCo_0.2O₂ (0.0000≤y≤0.0100) compositions were synthesized by a conventional solid-state method. The products were characterized by XRD, galvanostatic cycling, cyclic voltammetry, electrochemical impedance spectroscopy and thermal analysis. For the LiZn_0.0025Ni_0.7975Co_0.2O₂ system cycled between 3.0 and 4.2 V, the discharge capacities in the 1st and 100th cycles were 170 and 138 mAh/g with charge retention of 81%. The corresponding values for the undoped material were 158 and 97 mAh/g, with charge retention of 61.4%. The improved electrochemical properties of the doped system were attributed to the structural stability derived from incorporating the size-invariant Zn²⁺ ions. The Zn-doped system also showed improved capacity and cyclability when the cycling was performed in a voltage wider window (2.5–4.4 V) and at a higher temperature (55 °C). The structural and electrochemical properties of the doped and undoped materials were correlated.     

Construction of Li-ion supercapacitor-type battery using active carbon/LiNi0.5Co0.2Mn0.3O2 composite as cathode and its electrochemical performances

采用有机体系（NMP+PVDF）混料及乙醇萃取的方法成功制得活性炭/LiNi_0.5Co_0.2Mn_0.3O₂（AC/NCM）复合电极片,通过设计不同AC/NCM配比能够调控能量和功率密度。选取AC/NCM为1/3配比的复合正极和硬碳（HC）负极组装的超级电容电池循环伏安（CV）曲线呈现近似矩形的容性特征,恒流充放电过程电压随时间的变化（V-t曲线）呈现出良好的线性行为。此外,采用导电炭黑（SP）/碳纳米管（CNT）/石墨烯（graphene）=3/1/1的质量比设计了复合导电剂,立体导电网络的构建有效降低了器件内阻。按照IEC 62660—1标准,在2.5～4.2 V电压窗口,83.4 W/kg功率密度下测得的能量密度高达66.6 W·h/kg,在最大功率密度6.5 kW/kg下测得的能量密度为21.5 W·h/kg。器件充满电后在65℃高温存储168 h能量保有率为97.4%,且无任何胀气现象,平均自放电率为27.5 mV/天,表现出优良的高温特性。采用14 C和50 C电流循环充放电1000次后能量保有率分别为99.06%和96.45%,体现出该超级电容电池的长寿命优势。在12 kW/kg平均放电功率密度下进行脉冲测试,连续放电100次后该器件仍表现出良好的稳定性,表明在车辆启动、脉冲器件等领域具有极大的应用潜力。     

Influence of synthesis conditions on electrochemical properties of high-voltage Li1.02Ni0.5Mn1.5O4 spinel cathode material

Li_1.02Ni_0.5Mn_1.5O₄ spinel cathode materials were successfully synthesized by a citric acid-assisted sol-gel method. The structure and morphology of the materials have been examined by X-ray diffraction and scanning electron microscopy, respectively. Electrochemical properties of the materials were investigated using cyclic voltammetry and galvanostatic charge/discharge measurements at two different temperatures (25 and 55 °C) using lithium anode. The initial capacity and capacity retention are highly dependent on the particle size, particle size distribution, crystallinity and purity of the materials. The Li_1.02Ni_0.5Mn_1.5O₄ materials synthesized both at 800 and 850 °C have shown best electrochemical performance in terms of capacity and capacity retention between 3.5 and 4.9 V with a LiPF₆ based electrolyte.     

Preparation and electrochemical performances of Ni-rich LiNi0.91Co0.06Mn0.03O2 cathode for high-energy LIBs

One important challenge of lithium ion batteries is to improve the energy density while maintaining long-term cyclability. The energy density is strongly dependent on the Ni content in LiNi_1-x-yCo_xMn_yO₂. Herein, Ni-rich LiNi_0.91Co_0.06Mn_0.03O₂ has been synthesized as a high energy cathode material by co-precipitation method and the electrochemical performance of the LiNi_0.91Co_0.06Mn_0.03O₂ has been investigated. The granule morphology LiNi_0.91Co_0.06Mn_0.03O₂ with high crystallinity is obtained and which delivers a discharge capacity of 208.3 mA h g⁻¹ with cyclability of 61.9%, after 100 cycles and rate performance of 85.6%, at 2 C. These findings indicate that LiNi_0.91Co_0.06Mn_0.03O₂ is one of the promising candidate cathode for high-energy lithium ion batteries.     

Electrode performance of layered LiNi0.5Ti0.5O2 prepared by ion exchange

A layered Li–Ni–Ti oxide including divalent nickel and tetravalent titanium with a Ni²⁺/Ti⁴⁺ ratio of almost 1 was obtained by the ion exchange of a layered Na–Ni–Ti oxide precursor. By using various nickel and titanium sources, we obtained samples with different specific surface areas. Sample with larger specific surface areas had larger first charge capacities. However, a large irreversible capacity and poor cyclability were observed for all the samples when measured at room temperature. However, when we set the ambient temperature at 55 °C, the cyclability improved. This suggests that the lithium diffusion rate strongly affects the electrode performance of layered Li–Ni–Ti oxide. We also employed a first-principles calculation of the LiNi_0.5Ti_0.5O₂/Ni_0.5Ti_0.5O₂ system to evaluate its structural and voltage characteristics.     

Improved electrochemical properties of BiOF-coated 5 V spinel Li[Ni0.5Mn1.5]O4 for rechargeable lithium batteries

The electrochemical properties of BiOF-coated 5 V spinel Li[Ni_0.5Mn_1.5]O₄ were investigated at elevated temperatures (55 °C). As observed by scanning and transmission electron microscopy, BiOF nanolayers with ∼10 nm thickness were coated on the surface of Li[Ni_0.5Mn_1.5]O₄. The BiOF coating layer protected the surface of the active materials from HF generated by the decomposition of LiPF₆ in the electrolyte during electrochemical cycling. The dissolution of transition metal elements was also suppressed upon cycling. Therefore, the capacity retention of the BiOF-coated Li[Ni_0.5Mn_1.5]O₄ was obviously improved compared to the pristine Li[Ni_0.5Mn_1.5]O₄ at 55 °C.     

Preparation and electrochemical/thermal properties of LiNi0.74Co0.26O2 cathode material

Electrochemical and thermal properties of LiNi_0.74Co_0.26O₂ cathode material with 5, 13 and 25 μm-sized particles have been studied by using a coin-type half-cell Li/LiNi_0.74Co_0.26O₂. The specific capacity of the material ranges from 205 to 210 mA h g⁻¹, depending on the particle size or the Brunauer, Emmett and Teller (BET) surface area. Among the particle sizes, the cathode with a particle size of 13 μm shows the highest specific capacity. Even though the material with a particle size of 5 μm exhibits the smallest capacity value of 205 mA h g⁻¹, no capacity fading was observed after 70 cycles between 4.3 and 2.75 V at the 1 C rate. Differential scanning calorimetry (DSC) studies of the charged electrode at 4.3 V show a close relationship between particle size (BET surface area) and thermal stability of the electrode, namely, a larger particle size (smaller BET surface area) leads to a better thermal stability of the LiNi_0.74Co_0.26O₂ cathode.