Layer by layer synthesis of Sn-Co-C microcomposites and their application in lithium ion batteries

Alloy anodes were studied for pursuing Sn-based microcomposite synthesis, assembly and performance for lithium ion batteries. The self-assembled Sn-Co-C composites with nano-scaled microstructures were prepared via solution method and carbothermal technology. The morphology and physical structure were investigated with scanning electron microscope (SEM) and X-ray diffraction (XRD). The as-prepared materials were assembled to half cell coin for the purpose of discussing the galvanostatic cycling, cyclic voltammetry and rate-capability performance. Results reveal that nanoscaled CoSn 2 alloys covered with Sn and C layer by layer are wrapped by cross-linked porous carbon network to form spherical microstructure. This distinguishing feature of Sn-Co-C composites provides a possible solution to the problems of Sn particle aggregation and poor electron transport, and has strong effect on improving electrochemical performance.

Fast-ionic conductor Li_(2.64)(Sc_(0.9)Ti_(0.1))_(2)(PO_(4))_(3) doped PVDF-HFP hybrid gel-electrolyte for lithium ion batteries

With increasing demand on energy density of lithium-ion battery,wide electrochemical window and safety performance are the crucial request for next generation electrolyte.Gel-electrolyte as a pioneer for electrolyte solidization development aims to solve the safety and electrochemical window problems.However,low ionic conductivity and poor physical performance prohibit its further application.Herein,a fast-ionic conductor(Li_(2.64)(Sc_(0.9)Ti_(0.1))_(2)(PO_(4))_(3))(LSTP)was added into poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP)base gel-electrolyte to enhance mechanical properties and ionic conductivity.Evidences reveal that LSTP was able to weaken interforce between polymer chains,which increased the ionic conductibility and decreased interface resistance during the cycling significantly.The obtained LiFePO_(4)/hybrid gel-electrolyte/Li-metal coin cell exhibited excellent rate capacity(145 mA·h/g at 1C,95 mA·h/g at 3C,28℃)which presented a potential that can be comparable with commercialized liquid electrolyte system.

Electrochemical performances of NiO/Ni2N nanocomposite thin film as anode material for lithium ion batteries

Despite the high specific capacities,the practical application of transition metal oxides as the lithium ion battery(LIB)anode is hindered by their low cycling stability,severe polarization,low initial coulombic efficiency,etc.Here,we report the synthesis of the NiO/Ni2N nanocomposite thin film by reactive magnetron sputtering with a Ni metal target in an atmosphere of 1 vol.% O2 and 99 vol.%N2.The existence of homogeneously dispersed nano Ni2N phase not only improves charge transfer kinetics,but also contributes to the one-off formation of a stable solid electrolyte interphase(SEI).In comparison with the NiO electrode,the NiO/Ni2N electrode exhibits significantly enhanced cycling stability with retention rate of 98.8%(85.6%for the NiO electrode)after 50 cycles,initial coulombic efficiency of 76.6%(65.0%for the NiO electrode)and rate capability with 515.3 mA·h·g^−1(340.1 mA·h·g^−1 for the NiO electrode)at 1.6 A·g^−1.

Preparation and electrochemical performance of MWCNTs@MnO_2 nanocomposite for lithium ion batteries

Tubular nanocomposite with interconnected MnO2 nanoflakes coated on MWCNTs(MWCNTs@MnO2)was fabricated by an aqueous solution method at 80°C.Scanning electron microscopy,X-ray diffraction and galvanostatic charge-discharge tests were used to characterize the structures and electrochemical performances of the as-prepared nanocomposite.The capacity reaches 1233.6 mA h g-1 at a current density of 100 mA g-1 for the first discharge,and it can still maintain a capacity of 633.1mA h g-1 after 100 charge-discharge cycles.The results show that MWCNTs with good electrical conductivity as anchors of MnO2 can provide fast electron transport channels for MnO2 in the electrochemical reactions,and the as-prepared MWCNTs@MnO2 nanocomposite is a potential anode material for lithium ion batteries.

Electrochemical performance of Li_(2)O-V_(2)O_(5)-SiO_(2)-B_(2)O_(3) glass as cathode material for lithium ion batteries

A series of 20Li_(2)O-30V_(2)O_(5)-(50-x)SiO_(2)-xB_(2)O_(3)(mol.%)(x=10,20,30,40)glasses were prepared by the traditional melt-quenching synthesis.The amorphous nature of the glasses was determined by XRD,DSC and TEM investigations.FTIR measurement revealed the functional group of obtained glasses.And EDS results confirmed the presence and uniform distribution of elements in the glasses.20Li_(2)O-30V_(2)O_(5)-40SiO_(2)-10B_(2)O_(3)(LVSB10)sample with the highest V^(4+) ratio exhibited the best cycling capacity.In order to further improve cycling stability of LVSB10 sample,ball milling was employed to reduce the particle size.The ball milled LVSB10 sample(LVSB10-b)showed an improved first discharge capacity,cycling stability and rate capacity.EIS measurements showed that ball milling can effectively decrease charge transfer impedance and facilitate Li^(+) ion diffusion.This work provides a new way to explore a new type of cathode materials for lithium ion batteries.

Characterization and Electrochemical Performance of ZnO Modified LiFePO_4/C Cathode Materials for Lithium-ion Batteries

To improve the electrical conductivity of LiFePO4 cathode materials, the ZnO modified LiFePO4/C cathode materials are synthesized by a two-step process including solid state synthesis method and precipitation method. The structures and compositions of ZnO modified LiFePO4/C cathode materials are characterized and analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy, which indicates that the existence of ZnOhas little or no effect on the crystal structure, particles size and morphology of LiFePO4. The electrochemical performances are also characterized and analyzed with charge-discharge test, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the existence of ZnO improves the specific capability and lithium ion diffusion rate of LiFePO4 cathode materials and reduces the charge transfer resistance of cell, and the one with 3 wt% ZnO exhibits the best electrochemical performance.

Biomass-derived nitrogen-doped hierarchical porous carbon as efficient sulfur host for lithium–sulfur batteries

Lithium-sulfur(Li-S) battery is a potential energy storage technology with high energy density and low cost. However, the gap between theoretical expectation and practical performance limits its wide implementation. Herein, we report a nitrogen-doped porous carbon derived from biomass pomelo peel as sulfur host material for Li-S batteries. The hierarchical porous architecture and the polar surface introduced by N-doping render a favorable combination of physical and chemical sulfur confinements as well as an expedite electron/ion transfer, thus contributing to a facilitated and stabilized sulfur electrochemistry. As a result, the corresponding sulfur composite electrodes exhibit an ultrahigh initial capacity of 1534.6 mAh g^-1, high coulombic efficiency over 98% upon 300 cycles, and decent rate capability up to 2 C. This work provides an economical and effective strategy for the fabrication of advanced carbonaceous sulfur host material as well as the significant improvement of Li-S battery performance.

Recent progress of surface coating on cathode materials for high-performance lithium-ion batteries

Lithium-ion batteries (LIB) have received substantial attention in the last 10 years,as they offer great promise as power sources that can lead to the electric vehicle (EV) revolution in the next 5 years.Since the cathode serves as a key component in LIB,its properties significantly affect the performance of the whole system.Recently,the cathode surface modification based on coating technique has been widely employed to enhance the electrochemical performances by improving the material conductivity,stabilising the physical structure of materials,as well as preventing the reactions between the electrode and electrolyte.In this work,we reviewed the present of a number of promising cathode materials for Li-ion batteries.After that,we summarized the very recent research progress focusing on the surface coating strategies,mainly including the coating materials,the coating technologies,as well as the corresponding working mechanisms for cathodes.At last,the challenges faced and future guidelines for optimizing cathode materials are discussed.In this study,we propose that the structure of cathode is a crucial factor during the selection of coating materials and technologies.

Synthesis and electrochemical performances of high-voltage LiNi_0.5Mn_1.5O_4 cathode materials prepared by hydroxide co-precipitation method

Spherical cathode material LiNi_0.5Mn_1.5O_4 for lithium-ion batteries was synthesized by hydroxide co- precipitation method. X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical mea- surements were carried out to characterize prepared LiNi_0.5Mn_1.5O_4 cathode material. SEM images show that the LiNi_0.5Mn_1.5O_4 cathode material is constituted by micro-sized spherical particles （with a diameter of around 8 μm）. XRD patterns reveal that the structure of prepared LiNi_0.5Mn_1.5O_4 cathode material belongs to Fd3m space group. Electrochemical tests at 25℃show that the LiNi_0.5Mn_1.5O_4 cathode material prepared after annealing at 600 ℃ has the best electrochemical performances. The initial discharge capacity of prepared cathode material delivers 113.5 mAh·g-1 at 1C rate in the range of 3.50-4.95 V, and the sample retains 96.2% （1.0C） of the initial capacity after 50 cycles. Under different rates with a cutoff voltage range of 3.50-4.95 V at 25℃, the dis- charge capacities of obtained cathode material can be kept at about 145.0 （0.1C）, 126.8 （0.5C）, 113.5 （1.0C） and 112.4mAh·g-1 （2.0C）, the corresponding initial coulomb efficiencies retain above 95.2% （0.1C）, 95.0% （0.5C）, 92.5% （1.0C） and 94.8% （2.0C）, respectively.

Preparation and electrochemical properties of carbon-coated LiFePO_4 hollow nanofibers

Carbon-coated LiFePO_4 hollow nanofibers as cathode materials for Li-ion batteries were obtained by coaxial electrospinning. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller specific surface area analysis, galvanostatic charge–discharge, and electrochemical impedance spectroscopy（EIS） were employed to investigate the crystalline structure, morphology, and electrochemical performance of the as-prepared hollow nanofibers. The results indicate that the carbon-coated LiFePO_4 hollow nanofibers have good long-term cycling performance and good rate capability： at a current density of 0.2C（1.0C = 170 mA ·g^-1） in the voltage range of 2.5–4.2 V, the cathode materials achieve an initial discharge specific capacity of 153.16 mA h·g^-1 with a first charge–discharge coulombic efficiency of more than 97%, as well as a high capacity retention of 99% after 10 cycles; moreover, the materials can retain a specific capacity of 135.68 mA h·g^-1, even at 2C.

Porous V_2O_5-SnO_2 /CNTs composites as high performance cathode materials for lithium-ion batteries

Vanadium pentoxide （V205） exhibits high theoretical capacities when used as a cathode in lithium ion batteries （LIBs）, but its application is limited by its structural instability as well as its low lithium and electronic conductivities. A porous composite of V2Os-SnO2/carbon nanotubes （CNTs） was prepared by a hydrothermal method and followed by thermal treatment. The small particles of V205, their porous structure and the coexistence of SnO2 and CNTs can all facilitate the diffusion rates of the electrons and lithium ions. Electrochemical impedance spectra indicated higher ionic and electric conductivities, as compared to commercial V205. The VzOs-SnOz/CNTs composite gave a reversible discharge capacity of 198 mAh.g- 1 at the voltage range of 2.05-4.0 V, measured at a current rate of 200 mA.g-1, while that of the commercial V205 was only 88 mAh.g-1, demonstrating that the porous V2Os-SnOz/CNTs composite is a promising candidate for high-performance lithium secondary batteries.

Effects of synthesis conditions on the structural and electrochemical properties of layered LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2 cathode material via oxalate co-precipitation method

The uniform layered LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion batteries was prepared by using （Ni1/3Co1/3Mn1/3）C2O4 as precursor synthesized via oxalate co-precipitation method in air. The effects of calcination temperature and time on the structure and electrochemical properties of the LiNi1/3Co1/3Mn1/3O2 were systemically studied. XRD results revealed that the optimal calcination conditions to prepare the layered LiNi1/3Co1/3Mn1/302 were 950℃ for 15 h. Electrochemical measurement showed that the sample prepared under the such conditions has the highest initial discharge capacity of 160.8 mAh/g and the smallest irreversible capacity loss of 13.5% as well as stable cycling performance at a constant current density of 30 mA/g between 2.5 and 4.3 V versus Li at room temperature.

Electrochemical performance of LiFePO_4 cathode material for Li-ion battery

In the search for improved materials for rechargeable lithium batteries, LiFePO4 offers interesting possibilities because of its low raw materials cost, environmental friendliness and safety. The main drawback with using the material is its poor electronic conductivity and this limitation has to be overcome. Here Al-doped LiFePO4/C composite cathode materials were prepared by a polymer-network synthesis technique. Testing of X-ray diffraction, charge-discharge, and cyclic voltammetry were carried out for its performance. Results show that Al-doped LiFePO4/C composite cathode materials have a high initial capacity, good cycle stability and excellent low temperature performance. The electrical conductivity of LiFePO4 material can be obviously improved by doping Al. The better electrochemical performances of Al-doped LiFePO4/C composite cathode materials have a connection with its conductivity.

Precise carbon structure control by salt template for high performance sodium-ion storage

Carbon materials are considered to be one of the most promising anode materials for sodium-ion batteries(SIBs),but the well-ordered graphitic structure limits the intercalation of sodium ions.Besides,the sluggish intercalation kinetics of sodium ions impedes the rate performance.Thus,the precise structure control of carbon materials is important to improve the battery performance.Herein,a 3D porous hard-soft composite carbon(3DHSC)was prepared using the NaCl as the template and phenolic resin and pitch as carbon precursors.The NaCl template restrains the growth of the graphite crystallite during the carbonization process,resulting in small graphitic domains with expanded interlayer spacing which is favorable for the sodium storage.Moreover,the Na Cl templates help to create abundant mesopores and macropores for fast sodium ion diffusion.The porous structure and the graphite crystalline structure can be precisely controlled by simply adjusting the mass ratio of Na Cl,and thus,the suitable structure can be prepared to reach high capacity and rate performance while keeping a relatively high Coulombic efficiency.Typically,a high reversible capacity(215 mA h g^(-1)at 0.05 A g^(-1)),an excellent rate capability(97 mA h g^(-1)at 5 A g^(-1)),and a high initial Coulombic efficiency(60%)are achieved.

Hybrid co-based MOF nanoboxes/CNFs interlayer as microreactors for polysulfides-trapping in lithium-sulfur batteries

Lithium-sulfur battery is desirable for the future potential electrochemical energy storage device with advantages of high theoretical energy density,low cost and environmental friendliness.However,some natural hindrances,particularly fast capacity degradation resulting from the migration of dissolved polysulfide intermediates,remain to be significant challenges prior to the practical applications.In this work,a composite interlayer of carbon nanofibers(CNFs)which are enriched by Co-based metal organic frameworks(ZIF-67)growth in-situ is exploited.Notably,physical blocking and chemical trapping abilities are obtained synergistically from the ZIF/CNFs interlayer,which enables to restrain the dissolution of polysulfides and alleviate shuttle effect.Moreover,the three-dimensional fiber networks provide an interconnected conductive framework between each ZIF microreactor to promote fast electron transfer during cycling,thus contributing to excellent rate and cycling performance.As a result,Li-S cells with ZIF/CNFs interlayer show a high specific capacity of 1334 mAh g^(-1) at 1 C with an excellent cycling stability over 300 cycles.Besides,this scalable and affordable electrospinning fabrication method provides a promising approach for the design of MOFs-derived carbon materials for high performance Li-S batteries.

Physical and Electrochemical Characterization of Hydrothermal Prepared α'-NaV_2O_5 Crystals

a＇-NaV2O5 was prepared by a simple hydrothermal process. X-ray diffraction confirmed the orthorhombic structure of a＇-NaV2O5, with preferential growth along the （001） direction. Scanning electron microscopy showed a＇-NaV205 was composed of flake-shaped crystals. X-ray photoelectron spectroscopy confirmed the co-existence of V^4＋ and V^5＋ in a＇-NaV2O5, which results in an average V^4.5＋ oxidation state of a＇-NaV2O5. The observed Raman bands are ascribed to different V-O vibrations, a＇-NaV205 shows a reversible specific capacity of about 100 mA·h·g^-1 between 3.5 and 1.0 V, with a good capacity retention. The good electrochemical stability of the material is attributed to its structural stability during Li^＋ intercalation.

Influence of pretreatment process on structure, morphology and electrochemical properties of Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_2 cathode material

The layered Li[Ni1/3Mn1/3Co1/3]O2 was separately synthesized by pretreatment process of ball mill method and solution phase route, using [Ni1/3Co1/3Mn1/3]3O4 and lithium hydroxide as raw materials. The physical and electrochemical behaviors of Li[Ni1/3Mn1/3Co1/3]O2 were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, field emission scanning electron microscopy （FESEM） and electrochemical charge/discharge cycling tests. The results show that the difference in pretreatment process results in the difference in compound Li[Ni1/3Co1/3Mn1/3]O2 structure, morphology and the electrochemical characteristics. The Li[Ni1/3Mn1/3Co1/3]O2 prepared by solution phase route maintains the uniform spherical morphology of the [Ni1/3Co1/3Mn1/3]3O4, and it exhibits a higher capacity retention and better rate capability than that prepared by ball mill method. The initial discharge capacity of this sample reaches 178 mA-h/g and the capacity retention after 50 cycles is 98.7% at a current density of 20 mA/g. Moreover, it delivers high discharge capacity of 135 mA-h/g at a current density of 1 000 mA/g.

NiCuCoMn电极材料的制备及其储锂性能研究

采用熔炼甩带和化学脱合金相结合的方法制备纳米多孔NiCuCoMn过渡金属氧化物(NiCuCoMn@TMOs),并通过热处理进一步制备R-NiCuCoMn@TMOs。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)等测试对材料进行结构表征并对其进行电化学性能测试。作为锂离子电池负极材料,R-NiCuCoMn@TMOs在0.1 A/g的电流密度下,经过200次循环后具有394.9 mAh/g的高比容量,并且表现出97.53%的优异容量保持率。与热处理前相比,热处理后的材料具有更丰富的氧空位、更低的电荷转移电阻(38Ω)和更优异的倍率性能(在2 A/g的电流密度下,比容量为141.1 mAh/g)。其独特的纳米多孔结构提供了丰富的反应活性位点;不同半径、价态和反应电位的多种金属阳离子的协同效应使得该材料有很好的体积容忍度以适应脱嵌锂过程中的体积变化,表现出优异的电化学性能。此外,该电极材料原料储量丰富,价格低廉,易于实现批量化制备。该工作为设计多组元过渡金属氧化物负极材料提供了新的思路。

C/Sn复合薄膜的磁控溅射制备及其作为锂离子电池负极材料的电化学性能

采用磁控溅射的方法在铜箔上制备了C/Sn复合薄膜并将其作为锂离子电池负极材料,研究了C/Sn复合薄膜中Sn质量分数对其电化学性能的影响。研究发现,随着复合薄膜中Sn质量分数的增加,其首圈放电比容量增加,在一定范围内增加Sn质量分数,首圈库仑效率增加,但当Sn质量分数过多时其库仑效率降低。Sn质量分数分别为89.20%、91.61%、93.85%、95.81%的四种复合薄膜,在电流密度为500 mA/g时的首圈放电比容量分别为1195.4、1372.97、1574.86、1642.30 mA·h/g,首圈库仑效率分别为86.84%、87.88%、94.06%、80.66%。循环200圈后,四种复合薄膜的比容量衰减率分别为0.70%、6.13%、11.32%、18.88%。研究结果表明,当复合薄膜中Sn质量分数为89.20%时,其具有最优的倍率性能和循环稳定性能,随着复合薄膜中Sn质量分数的增加,其倍率性能及循环稳定性变差。

木质素基碳/硫纳米球复合材料作为高性能锂硫电池正极材料

锂硫二次电池因具有非常高的理论比容量(1675 mAh/g)和能量密度(2600 Wh/kg)而备受关注。然而,锂硫电池的正极材料单质硫因导电性差和在充放电过程中生成的多硫化物Li_(2)S_(n)(4≤n≤8)极易发生“穿梭效应”等问题,严重降低了对活性硫的利用效率,造成电极材料不可逆的容量损失。因此寻找成本低、可循环利用、热稳定性好的碳载体基质是提高锂硫电池电化学性能最有效的方法之一。在本研究中,以天然木质素作为碳源,首先经过萃取和碳化过程制备了多孔碳纳米球,再通过熔融过程,将单质硫成功地包裹进木质素基碳纳米球的孔隙中,制备得到多孔球状结构的碳/硫复合材料(LS-C/S)。当该复合材料用作锂硫电池正极材料时,在0.1 C电流密度下,硫含量为59.41%(质量分数)的电极材料的首次放/充电比容量分别为800.3 mAh/g和758.8 mAh/g,对应库仑效率为94.8%,在经过200次充放电循环后,其比容量稳定在647.4 mAh/g,容量保持率为84.3%,相当于每循环一圈容量平均损失为0.0785%。此外,在经过高倍率的充放电循环后,比容量仍能恢复并稳定在620 mAh/g,展现出良好的可逆倍率稳定性。这种木质素基碳纳米球具有的高比表面积和多孔结构,促进了锂离子和电子的传输,有效地抑制了中间产物多硫化锂的溶解扩散,提高了单质硫作为正极材料的利用效率,因此,复合材料表现出优异的循环稳定性和可逆倍率性能。