Synergistic effect of bulk phase doping and layered-spinel structure formation on improving electrochemical performance of Li-Rich cathode material

In this study, La was doped into the lithium layer of Li-rich cathode material and formed a layered-spinel hetero-structure. The morphology, crystal structure, element valence and kinetics of lithium ion migration were studied by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The La doped lithium-rich cathode material exhibited similar initial discharge capacity of 262.8 mAh g^?1 at 0.1 C compared with the undoped material, but the discharge capacity retention rate can be obviously improved to 90% after 50 cycles at 1.0 C. Besides that, much better rate capability and Li⁺ diffusion coefficient were observed. The results revealed that La doping not only stabilized the material structure and reduced the Li/Ni mixing degree, but also induced the generation of spinel phase to provide three-dimensional diffusion channels for lithium ion migration. Moreover, the porous structure of the doped samples also contributed to the remarkable excellent electrochemical performance. All of these factors combined to significantly improve the electrochemical performance of the material.     

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.     

Electrospinning synthesis of novel lithium-rich 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 nanotube and its electrochemical performance as cathode of lithium-ion battery

In this study, a lithium-rich layered 0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂ nanotube cathode synthesized by novel electrospinning is reported, and the effects of temperature on the electrochemical performance and morphologies are investigated. The crystal structure is characterized by X-ray diffraction patterns, and refined by two sets of diffraction data (R-3m and C2/m). Refined crystal structure is 0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂ composite. The inductively coupled plasma optical emission spectrometer and thermogravimetric and differential scanning calorimetry analysis measurement supply reference to optimize the calcination temperature and heat-treatment time. The morphology is characterized by scanning and highresolution transmission electron microscope techniques, and the micro-nanostructured hollow tubes of Li-rich 0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂ composite with outer diameter of 200-400 nm and the wall thickness of 50-80 nm are synthesized successfully. The electrochemical evaluation shows that 0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂ sintered at 800 ℃ for 8 h delivers the highest capacity of the first discharge capacity of 267.7 mAh/g between 2.5 V and 4.8 V at 0.1C and remains 183.3 mAh/g after 50 cycles. The electrospinning method with heat-treatment to get micro-nanostructured lithium-rich cathode shows promising application in lithium-ion batteries with stable electrochemical performance and higher C-rate performance for its shorter Li ions transfer channels and stable designed structure.     

A comparison of preparation method on the electrochemical performance of cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 for lithium ion battery

Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ as a cathode material for Li-ion battery has been successfully prepared by co-precipitation (CP), sol–gel (SG) and sucrose combustion (SC) methods. The prepared materials were characterized by XRD, SEM, BET and electrochemical measurements. The XRD result shows that the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ materials prepared by different methods all form a pure phase with good crystallinity. SEM images and BET data present that the SC-material exhibited the smallest particle size (ca. 0.1 μm) and the highest surface area (7.4635 m² g⁻¹). The tap density of SC-material is lower than that of CP- and SG-materials. The result of rate performance tests indicates that the SC-material showed the best rate capability with the highest discharge capacity of 178 mAh g⁻¹ at 5.0 C, followed by SG-material and then CP-material. However, the cycling stability of SC-material tested at 0.1 and 0.5 C is relatively poor as compared to that of SG-material and CP-material. The result of EIS measurements reveals that large surface area and small particle size of the SC-electrode result in more SEI layer formation because of the increased side reactions with the electrolyte during cycling, which deteriorates the electrode/electrolyte interface and thus leads to the faster capacity fading of the SC-material.     

Influence of different lithium sources on the morphology,structure and electrochemical performances of lithium-rich layered oxides

Lithium-rich layered oxides were synthesized via co-precipitation by using different lithium sources (LiOH, Li₂CO₃ and CH₃COOLi). Scanning electron microscope (SEM), Thermo gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), Inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD) and electrochemical measurements were used to investigate the morphology, reaction process, specific surface area, composition, structure and electrochemical performance of the lithium-rich oxides, respectively. The use of different lithium sources mainly affects the primary particle size and secondary particle morphology of the final product. Using LiOH as the lithium source, the maximum discharge capacity of sample can reach to 272.1 mA h g^–1 in the voltage range of 2.0–4.6 V at room temperature, even after 50 cycles, the retention rate is still reach 91.4%. The electrochemical impedance spectroscopy (EIS) results show that lithium-rich oxides using LiOH as the lithium source have the minimum value of impedance after 50 cycles. Therefore, the choice of appropriate lithium source is an effective way to improve the electrochemical properties of lithium-rich layered oxides.     

Sol-gel synthesis of nano Li1.2Mn0·54Ni0·13Co0·13O2 cathode materials using DL-lactic acid as chelating agent

Lithium-rich cathode materials Li_1·2Mn_0·54Ni_0·13Co_0·13O₂ (LMNCO) are prepared by sol-gel method using dl-lactic acid as chelating agent. The effect of pH on crystal structures, morphologies, particle sizes, and electrochemical properties of cathode materials are studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM), nanoparticle analysis, charge–discharge tests, and electrochemical analysis. The Li_1·2Mn_0·54Ni_0·13Co_0·13O₂ cathodes exhibit well-ordered layered structures consisting of hexagonal LiMO₂ and monoclinic Li₂MnO₃ with smooth surfaces and well-crystallized particles (100–500 nm). LMNCO-7.0 exhibits smaller particle sizes than LMNCO-5.5 and LMNCO-8.5 and better electrochemical performance. The first discharge capacity and Coulombic efficiency of LMNCO-7.0 are 232.31 mAh g^?1 and 73.2%, respectively. After 50 cycles, discharge capacity of LMNCO-7.0 decrease to 194.93 mAh g^?1. LMNCO-7.0 cathode shows superior discharge capacity and rate performance due to its low charge transfer impedance and small average quasi-spherical particle diameter.     

Synergy effects on blending Li-rich and classical layered cathode oxides with improved electrochemical performance

Blending different cathode materials to construct composites can be in compatibility with their individual advantages to exhibit better electrochemical performances. In this study, we blend Li-rich and classical layered cathode materials to realize the suppression of voltage decay. The electrochemical results indicate that the composite electrodes show better capacity retention exceeding 90% after 100 cycles. More importantly, the cumulative voltage decay of the composite materials with different ratio are 280 mV and 140 mV for 100 cycles’ duration, which are much lower than that of the single component with 390 mV in Li-rich layered cathode, respectively. Based on the ex situ X-ray diffraction, the blended composites show the structural origin of synergy effect, which are like a pair of parallel resistors to reciprocally buffer the crystal structure change during the charge and discharge process between Li-rich and classical layered cathode materials. Blending of layered cathode oxide materials with the synergy effect provide a possible approach to achieve more excellent electrochemical performances in lithium-ion batteries.     

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.     

富锂锰基材料低首次库伦效率原因及改性策略

富锂锰基正极材料（xLi2MnO3·（1-x）LiTMO2,0相似文献   

Suppressing the voltage decay of lithium-rich cathode for Li-Ion batteries via Pt nanoparticles surface modification

Lattice oxygen undergoes redox reaction to achieve high specific capacity of the material in lithium-rich cathode oxides. However, irreversible oxygen loss causes a change in the crystal structure, and the cations migrate in the transition metal layer, resulting in a rearrangement of the electronic structure and ultimately a severe voltage decay. Herein, we introduce Pt nanoparticles with good catalytic activity and electrical conductivity into lithium-rich cathode materials to improve the loss of lattice oxygen for the first time. We have revealed that the evolution of the lattice structure after the lattice oxygen redox reaction is relatively stable in the lithium-rich oxide with Pt nanoparticles, which is in stark contrast to the apparently deformed crystal structure in the lithium-rich oxide without Pt. Pt-containing electrodes exhibit excellent high-capacity retention rate (more than 80% after 200 cycles), and voltage decay is significantly reduced (less than 0.4 V after 200 cycles). Our results highlight the role of Pt nanoparticles in alleviating the loss of lattice oxygen and stabilizing the crystal structure, which opens up the field of vision for the design of high-energy-density lithium rich cathode oxides with stable structure.