Electrochemical properties of poly(4,4′-diaminodiphenyl sulfone) as a cathode material of lithium secondary batteries

Doped poly(4,4′-diaminodiphenyl sulfone) (pDDS) is prepared for use as a cathode-active material of lithium secondary batteries by chemical oxidation method using ammonium persulfate initiator. The synthesized pDDS and doped pDDS are characterized by chemical structure analysis using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry shows that the doped pDDS has a typical pair of redox peaks at 3.75/3.15 V vs. Li/Li⁺, corresponding to charging/discharging of the lithium ion. The discharge capacity at low current rate (0.05 C-rate) achieves 31.5 and 24.3 mA h g^?1 in the initial and 50th cycles, respectively. The doped pDDS also shows good cycle performance and high-rate capability, making it appropriate as a cathode material of lithium secondary batteries.     

Al-doping induced superior lithium ion storage capability of LiNiO2 spheres

To optimize the performance of LiNiO₂ with minimal modification of the pristine structure, a facile solid-state approach, based on the interdiffusion of elements at the solid/solid interface, is developed to achieve uniformly Al-doped LiNiO₂ using alumina coated Ni(OH)₂ spheres as the precursor. The resulting LiNi_0.95Al_0.05O₂ material exhibits excellent discharge capacity (209.9 mAh g⁻¹ at 0.1 C) and cycling stability with a capacity retention of 85.10% after 200 cycles at 0.5 C. This is ascribed to the improved reversibility of the phase transitions by Al-doping as revealed by in-situ XRD characterization. The Al-doping also endows the material with superior rate capability due to the enlarged interlayer spacing in the structure and alleviation of the side reactions at the electrode/electrolyte interface, favorable for lithium ion diffusion. An optimal amount of doped Al is necessary for ensuring the structure stability and interface ionic conductivity of the LiNiO₂ spheres. Thus, the present strategy may provide an opportunity to optimize the performance of LiNiO₂, with uniform doping of a small amount of Al, producing a promising cathode material for advanced lithium ion batteries.     

Effective enhancement of the electrochemical properties for Na2FeP2O7/C cathode materials by boron doping

In recent years, the composite materials based on polyanionic frameworks as secondary sodium ion battery electrode material have been developed in large-scale energy storage applications due to its safety and stability. The Na₂FeP₂O₇/C (theoretical capacity 97 mA·h·g^-1) is recognized as optimum Na-storage cathode materials with a trade-off between electrode performance and cost. In the present work, The Na₂FeP₂O₇/C and boron-doped Na₂FeP_2-BO₇/C composites were synthesized via a novel method of liquid phase combined with high temperature solid phase. The non-metallic element B doping not only had positive influence on the crystal structure stability, Na⁺ diffusion and electrical conductivity of Na₂FeP₂O₇/C, but also contributed to the high-value recycling of B element in waste borax. The structure and electrochemical properties of the cathode material were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), The X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and charge/discharge cycling. The results showed that different amounts of boron doping had positive effects on the structure and electrochemical properties of the material. The initial charge/discharge performances of born doped materials were improved in comparison to the bare Na₂FeP₂O₇/C. The cycle performance of the Na₂FeP_1.95B_0.05O₇/C showed an initial reversible capacity of 74.8 mA·h·g^-1 and the high capacity retention of 91.8% after 100 cycles at 1.0 C, while the initial reversible capacity of the bare Na₂FeP₂O₇/C was only 66.2 mA·h·g^-1. The improvement of apparent Na⁺ diffusion and electrical conductivity due to B doping were verified by the EIS test and CVs at various scan rate. The experimental results from present work is useful for opening new insight into the contrivance and creation of applicable sodium polyanionic cathode materials for high-performance.     

Synthesis and characterization of Pt-doped LiFePO4/C composites using the sol–gel method as the cathode material in lithium-ion batteries

LiFePO₄/C and LiFe_0.96Pt_0.04PO₄/C nanocomposite cathode materials were synthesized using the sol–gel method in a nitrogen atmosphere. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Their electrochemical properties were investigated using galvanostatic charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The XRD results indicate that substituting iron with platinum does not destroy the structure of LiFePO₄, but expands the lattice parameters and enlarges the cell volume. The electrochemical results show that platinum doping improves the electrochemical performance of LiFePO₄/C particles owing to the expansion of the lattice structure, which provides more space for Li ion diffusion. The, larger lattice structure parameters of the LiFe_0.96Pt_0.04PO₄/C material result in a high discharge capacity of 166, 156, 142 and 140 mAh g^?1 at rates of 0.2, 1, 5, and 10 C, respectively, as compared to 164, 150, 120, and 105 mAh g^?1 for undoped LiFePO₄/C.     

掺杂改性LiFePO_4正极材料制备及表征

采用微波热合法制备了掺杂LiFePO4锂电池用正极材料。通过XRD、SEM表征了材料的晶体结构和形貌,采用恒电流充放电法研究了材料的电化学性能。XRD结果表明,掺杂后的材料晶相为橄榄石型磷酸铁锂;SEM测试结果表明,加热时间延长促使材料颗粒团聚长大,且结晶完整,颗粒分布均匀。对电池的电化学测试表明,制备的掺杂LiFePO4材料表现出优良倍率性能和循环稳定性,充放电比容量分别为131.7 mAh/g和123.8 mAh/g,10次循环后比容量没有明显衰减。     

Improving electrochemical performance of LiMnPO<Subscript>4</Subscript> by Zn doping using a facile solid state method

Olivine structure LiMnPO₄/C as cathode materials for Li-ion batteries were synthesized via a simple solidstate reaction. Improvement of the electrochemical performance of LiMnPO₄/C cathode material was realized significantly by the method of doping Zn. The obtained LiMn_0.95Zn_0.05PO₄/C electrode material was studied by the measurements of X-ray diffraction pattern, scanning electronic microscopy, electrochemical impedance spectroscopy and electrochemical performance. The results indicate that the LiMn_0.95Zn_0.05PO₄/C materials exhibit discharge specific capacity of 140.2 mA h g⁻¹ at 0.02 C rate and better rate capability. These excellent results are elucidated by EIS test, which showed that there was the decrease of charge transfer resistance and faster lithium-ion diffusion in LiMnPO₄/C cathode materials after Zn doping.     

Hydrolysis lignin: Electrochemical properties of the organic cathode material for primary lithium battery

Electrochemical energy production has been extensively used in large scale applications. At present, organic compounds are considered as efficient and environmentally friendly electrode materials. The paper describes the study of the possibility of using hydrolysis lignin as the lithium battery cathode material. Hydrolysis lignin features have been investigated by the impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The discharge performance of hydrolysis lignin-based lithium battery was investigated at room temperature using 1 M LiBF₄ in γ-butyrolacton electrolyte system. It was found that the specific capacity of hydrolysis lignin was equal to 450 mAh g⁻¹ at a discharge current density of 25 μA/cm². Two main voltage plateaus located at ∼1.8 and ∼1.1 V were observed. The chemical composition of cathode materials upon battery discharge down to 0.9 V was studied by the X-ray photoelectron spectroscopy and infrared spectroscopy. The suggestions on possible electrochemical reactions occurring in the lithium/hydrolysis lignin system were made on the basis of the products composition analysis. The results demonstrate the potential of hydrolysis lignin based batteries to be used as low-rate power sources.     

Synthesis of lithium rich layered oxides with controllable structures through a MnO2 template strategy as advanced cathode materials for lithium ion batteries

The electrochemical performance of lithium ion batteries depend largely on the structural properties of electrode materials. In this work, we propose an approach to synthesize lithium-rich layered oxides (LLOs) materials using a manganese dioxide (MnO₂) template strategy, which could control the structure and particle size of final products via choosing different MnO₂ templates. Through precisely optimizing, we successfully prepare cross-linked nanorods (CLNs) and agglomerate microrods (AMs) Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ cathode materials by using carbon-decorated MnO₂ nanowires and MnO₂ nanorods as templates, respectively. The lithium ion battery based on the CLNs exhibits excellent performance, delivering a high capacity of 286.2 mAh g⁻¹ at 0.1 C and 237.5 mAh g⁻¹ at 1 C. In addition, the device remains 98% and 89% of its initial capacity after 50 cycles at 0.1 C and 100 cycles at 1 C, respectively. The remarkable electrochemical performance can be mainly attributed to the cross-linked nanorods structure which can provide relatively shorter lithium ion diffusion length, larger reaction surface and more internal cavity. This universal structure engineering strategy may shed light on new material structures for high performance lithium-rich layered oxide cathode materials.     

Enhancement of the electrochemical performance of LiCoPO4 by Fe doping

LiCoPO₄ is an attractive cathode material, but it undergoes poor electronic conductivity and electrochemical performance. This performance is enhanced by substituting iron antisite Cobalt to reduce the direct interaction between the cathode and the electrolyte. Thus, LiCoPO₄ doped with Fe was synthesized by the microwave-assisted solvothermal route at 220 °C. According to X-ray diffraction analysis, a single orthorhombic Pn21a phase (a = 10.02 Å, b = 6.71 Å and c = 4.96 Å) was obtained, which transited to Pnma phase (a = 10.21 Å b = 5.92 Å and c = 4.76 Å) after annealing at 700 °C in air. The morphology and particle size of the sample changed after annealing, as shown by TEM. The electrochemical cycling of an annealed sample showed the initial discharge capacity of 125mAh g⁻¹ compared to 12 mAh g⁻¹ for the non-annealed sample, which can be regarded as a partial coating by FePO₄ as obtained from X-ray absorption spectroscopy analysis.     

Influence of Ti and Fe doping on the structural and electrochemical performance of LiCo0.6Ni0.4O2 cathode materials for Li-ion batteries

The combination of lithium cobalt oxide (LCO) and lithium nickel oxide (LNO) property for Li-ion batteries (LIB) brings a very promising cathode material, LiCo_1?xNi_xO₂ with a high specific reversible capacity and good cycling behaviour. Nonetheless, high toxic Co content and an instability of Li⁺/Ni²⁺ interaction in LiCo_1?xNi_xO₂ crystal structure paved the way for some modification for the development of this potential material. In this research, the self-propagating combustion method is used to reduce 40% Co content of LCO by replacing it with 40% Ni content resulting in cathode material with the stoichiometry of LiCo_0.6Ni_0.4O₂ (LCN). To improve the stability of the LiCo_0.6Ni_0.4O₂ structure, 5% of Ti and Fe was substituted at the Co site of the LCN material. The effect of these different cation substitutions (Ti⁴⁺ and Fe³⁺) on the structural and electrochemical performance of layered LiCo_0.6Ni_0.4O₂ cathode materials was investigated. Rietveld refinement revealed that Fe doped material has the longest atomic distance Li–O in the structure that allow better Li⁺ diffusion during intercalation/deintercalation to give an excellent electrochemical performance (138 mAhg^?1). After 50th cycle, it is found that the discharge cycling for Ti and Fe substituted materials were improved by more than 5% compared to pristine material. Both Ti and Fe doped materials were also having less than 13% of capacity fading indicates that the substitution of some Co with Ti and Fe are stable and can retain their electrochemical properties.     

Niobium doping of Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials with enhanced structural stability and electrochemical performance

Lithium-rich layered oxides with high energy density have been intensively investigated as advanced lithium-ion batteries cathode materials. However, capacity degradation and voltage decay caused by irreversible lattice oxygen loss and structural transformation during cycling restrict their application. Herein, we proposed a high valance cations Nb⁵⁺ doping strategy and synthesized a series of Li_1.2Mn_0.54-x/3Ni_0.13-x/3Co_0.13-x/3Nb_xO₂ (x = 0, 0.01, 0.02 and 0.03) cathode materials. The effects of Nb⁵⁺ doping on crystallographic structure and electrochemical property were systematically studied. In virtue of the large ionic radii and strengthened Nb–O bonds, the doped samples present commendable structural stability and expanded interlayer spacing for Li-ions migration, which ensures the upgraded cyclic stability and rate performance. In particular, the electrode with x = 0.02 delivers a discharge specific capacity of 265.8 mAh g^-1 at 0.2 C with decelerated voltage decay, while 86.9% capacity are remained after long-term cycles. Moreover, excellent discharge specific capacity of 153.4 mAh g⁻¹ is still attained at 5 C accompanied with enhanced Li-ion diffusion kinetics.     

Li6V10O28, a novel cathode material for Li-ion battery

A novel cathode material, lithium decavanadate Li₆V₁₀O₂₈ with a large tunnel within the framework structure for lithium ion battery has been prepared by hydrothermal synthesis and annealing dehydration treatment. The structure and electrochemical properties of the sample have been investigated. The novel material shows good reversibility for Li⁺ insertion/extraction and long cycle life. High discharge capacity (132 mAh/g) is obtained at 0.2 mA/cm² discharge current and potential range between 2.0 and 4.2 V versus Li⁺/Li. AC impedance of the Li/Li₆V₁₀O₂₈ cell reveals that the cathode process is controlled mainly by Li⁺ diffusion in the active material. The novel material would be a promising cathode material for Li-ion batteries.     

Enhanced electrochemical performance of layered Li-rich cathode materials for lithium ion batteries via aluminum and boron dual-doping

Lithium-rich layer oxides can possess satisfactory specific capacity but suffer from severe voltage attenuation and poor cycle stability. In this work, Al-B dual-doping technique is introduced to modify Li-rich layered oxide cathode materials. Cross-section scanning electron microscopy, Energy Disperse Spectroscopy and X-ray photoelectron spectroscopy results confirm that Al and B successfully doped into the interior of the bulk Li_1.2Ni_0.2MnO₂ particles, and the High-resolution transmission electron microscopy and X-ray diffraction Rietveld refinement results reveal that the c-axis distance of LMR-AB increases. The Al-B co-doped sample shows greatly enhanced electrochemical performance. Specifically, it exhibits of a discharge capacity of 120?mAh?g^?1 at 5?C and a capacity retention of 89.12% after 100 cycles at 1?C. The voltage decay is also greatly alleviated. The enhanced electrochemical performance of LMR-AB is due to the synergistic effects bought by the Al-B dual-doping, where increase of c-axis distance decreases Li⁺ intercalation/deintercalation barrier. B³⁺ doping into the tetrahedral site block the migration of TM ions and Al³⁺ act as pillars in the octahedral site, stabilizing the structure and suppressing the phase transition during cycling.     

SmPO4-coated Li1.2Mn0.54Ni0.13Co0.13O2 as a cathode material with enhanced cycling stability for lithium ion batteries

SmPO₄ coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were prepared by the precipitation method and calcined at 450 °C. The crystal structures and electrochemical properties of the pristine and coated samples are studied by X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, electron diffraction spectroscopy, galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). It has been found that the electrochemical performances of the Li-rich cathode material have been substantially improved by SmPO₄ surface coating. Especially, the 2 wt% SmPO₄-coated sample demonstrates the best cycling performance, with capacity retention of 88.4% at 1 C rate after 100 cycles, which is much better than that of 72.3% in the pristine sample. The improved electrochemical properties have been ascribed to the SmPO₄ coating layer, which not only stabilizes the cathode structure by decreasing the loss of oxygen, but also protects the Li-rich cathode material from side reaction with the electrolyte and increases the Li⁺ migration rate at the cathode interface.     

Rheological phase reaction synthesis and electrochemical performance of Li3V2(PO4)3/carbon cathode for lithium ion batteries

Monoclinic lithium vanadium phosphate/carbon (Li₃V₂(PO₄)₃/C) cathode has been synthesized for applications in lithium ion batteries, via a rheological phase reaction (RPR) method. The sample is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). This material exhibits high initial discharge capacity of 189 and 177 mAh g⁻¹ at 0.1 and 0.2 C between 3.0 and 4.8 V, respectively. Moreover, it displays good fast rate performance, which discharge capacities of 140, 133, 129 and 124 mAh g⁻¹ can be delivered after 100 cycles between 3.0 and 4.8 V vs. Li at a different rate of 0.5, 1, 2 and 5 C, respectively. The electrochemical impedance spectroscopy (EIS) is also investigated.     

Enhanced rate performance of carbon-coated LiNi0.5Mn1.5O4 cathode material for lithium ion batteries

Conductive carbon has been coated on the surface of LiNi_0.5Mn_1.5O₄ cathode material by the carbonization of sucrose for the purpose of improving the rate performance. The effect of carbon coating on the physical and electrochemical properties is discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), cycling and rate tests. Results demonstrate that the carbon coating can greatly enhance the discharge capacity, rate capability and cycling stability of the LiNi_0.5Mn_1.5O₄ without degrading the spinel structure. The sample modified with 1 wt.% sucrose displays the best performance. A large capacity of 130 mAh g⁻¹ at 1 C discharge rate with a high retention of 92% after 100 cycles and a stable 114 mAh g⁻¹ at 5 C discharge rate can be delivered. The remarkably improved rate properties of the carbon-coated samples are due to the suppression of the solid electrolyte interfacial (SEI) layer development and faster kinetics of both the Li⁺ diffusion and the charge transfer reaction.     

锂离子电池高镍三元正极材料LiNi0.8Co0.1Mn0.1O2的性能研究

富镍正极材料(LiNi0.8Co0.1Mn0.1O2)具有高容量的优点,是锂离子电池正极材料最有潜力的材料之一。为确定最佳合成条件,本工作研究了合成温度对材料性能的影响,并详细分析了材料电化学性能衰减的原因以及循环过程中材料结构的变化。采用热重/差示扫描量热法(TG/DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(HRTEM)、能谱仪(EDS)、X射线光电子能谱(XPS)等手段对合成的正极材料进行了物化表征,并对其电化学性能进行测试。结果表明,在低温段500℃保温4 h,高温段750℃保温14 h合成的正极材料NCM750在0.2 C首次放电比容量为186.2 mAh/g,首次充放电效率为82.5%,1 C放电比容量为185.1 mAh/g,100次循环后仍有175.2 mAh/g,容量保持率为95.2%。在此条件下合成的材料具有结构稳定,粒径均匀,电化学性能优异等优点,本工作对富镍正极材料的合成及结构变化进行研究,有助于加深对材料的了解。     

Tuning the crystal structure and oxygen defect by doping lithium vanadate

For its high specific discharge capacity and low working voltage, lithium vanadate is considered a promising anode material. However, inherent low conductivity and unsatisfactory cycle performance limit its further application. In this work, doping at the V site does not destroy the crystal structure of lithium vanadate but also increases the lattice volume. Moreover, the increased content of oxygen defect in the presence of redox reaction effectively improves the electrochemical properties of lithium vanadate. At the same time, the enhancement of hydrophilicity effectively improves the migration rate of ions. Among all LiLa_xV_3-xO₈ samples, LiLa_0.01V_2.99O₈ (LVO-La-10) demonstrates better rate and cycle performance. LVO-La-10 delivers specific discharge capacities of 93.5 mAh g¹ at 0.5 C, and 42.8 mAh g^?1 at 7 C, which is 17.4 and 16.7 mAh g^?1 larger than that of lithium vanadate, respectively. Moreover, the capacity retention rate of LVO-La-10 (87.8%) is still higher than that of lithium vanadate (75.8%) at the rate of 0.2 C after 100 cycles. This work exhibits that increasing the lattice volume and oxygen defect of lithium vanadate effectively improves its electrochemical performance.     

Three-dimensional lithium manganese phosphate microflowers for lithium-ion battery applications

The Polyvinylpyrrolidone (PVP)-assisted polyol process was employed for the synthesis of lithium manganese phosphate (LiMnPO₄) microflowers as a cathode material for Li-ion battery applications. LiMnPO₄ microflowers were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope-energy dispersion spectroscope, and impedance spectroscopy. The microflowers were highly porous with nanosized petals. CR2032 coin cells were fabricated using LiMnPO₄ microflowers’ sample and their battery characteristics were tested. The discharge capacity of LiMnPO₄ microflowers was found to be 164 mAh g⁻¹ at 0.1C. The observed high discharge capacity was attributed to the short diffusion length of Li-ion motion in the nanopetals of the LiMnPO₄ microflowers.     

Preparation of porous-structured LiFePO4/C composite by vacuum sintering for lithium-ion battery

The LiFePO₄/C (LFP/C) composite as a cathode material for lithium-ion battery was synthesized by solid-state reaction under vacuum sintering condition (20–5 Pa). The effects of vacuum sintering temperature and time on the phase composition, morphological structure, and electrochemical performance of LFP/C composite were investigated by X-ray diffraction, scanning electron microscopy, galvanostatic charge–discharge cycling test, and electrochemical impedance spectroscopy. The synthetic LFP/C composite possessed uniform particle-size distribution with porous architecture upon sintering at 650 °C for 12 h and thus exhibited the highest discharge capacity and best cycle performance. The complete decomposition of citric acid at a suitable temperature under vacuum condition resulted in the formation of porous structure. Compared with atmospheric argon sintering, vacuum sintering method led to the formation of porous architecture, the porous sample showed excellent cycle performance with less than 2% capacity loss after 80 cycles at 0.2 C, and reached the discharge specific capacity of 87.6 mAh g⁻¹ at 10 C rate, these are better than that of atmospheric argon sintering. The LFP/C composite prepared under vacuum sintering also reduced the optimum sintering temperature by nearly 100 °C compared with that prepared under atmospheric argon sintering.