Solid-state synthesis of Li[Li0.2Mn0.56Ni0.16Co0.08]O2 cathode materials for lithium-ion batteries

Layered Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode materials were synthesized via a solid-state reaction for Li-ion batteries, in which lithium hydroxide monohydrate, manganese dioxide, nickel monoxide, and cobalt monoxide were employed as metal precursors. To uncover the relationship between the structure and electrochemical properties of the materials, synthesis conditions such as calcination temperature and time as well as quenching methods were investigated. For the synthesized Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ materials, the metal components were found to be in the form of Mn⁴⁺, Ni²⁺, and Co³⁺, and their molar ratio was in good agreement with stoichiometric ratio of 0.56:0.16:0.08. Among them, the one synthesized at 800 °C for 12 h and subsequently quenched in air showed the best electrochemical performances, which had an initial discharge specific capacity and coulombic efficiency of 265.6 mAh/g and 84.0%, respectively, and when cycled at 0.5, 1, and 2 C, the corresponding discharge specific capacities were 237.3, 212.6, and 178.6 mAh/g, respectively. After recovered to 0.1 C rate, the discharge specific capacity became 259.5 mAh/g and the capacity loss was only 2.3% of the initial value at 0.1 C. This work suggests that the solid-state synthesis route is easy for preparing high performance Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode materials for Li-ion batteries.     

Mesoporous composite of LiFePO4 and carbon microspheres as positive-electrode materials for lithium-ion batteries

Mesoporous LiFePO4/C microspheres consisting of LiFePO4 nanoparticles are successfully fabricated by an eco-friendly hydrothermal approach combined with high-temperature calcinations using cost-effective LiOH and Fe3＋ salts as raw materials.In this strategy,pure mesoporous LiFePO4 microspheres,which are composed of LiFePO4 nanoparticles,were uniformly coated with carbon（1.5nm）.Benefiting from this unique architecture,these mesoporous LiFePO4/C microspheres can be closely packed,having high tap density.The initial discharge capacity of LiFePO4/C microspheres as positive-electrode materials for lithium-ion batteries could reach 165.3 mAh/g at 0.1 C rate,which is notably close to the theoretical capacity of LiFePO4 due to the large BET surface area,which provides for a large electrochemically available surface for the active material and electrolyte.The material also exhibits high rate capability（100 mAh/g at 8 C） and good cycling stability（capacity retention of 92.2%after 400 cycles at 8 C rate）.     

Si-induced insertion of Li into SiC to form Li-rich SiC twin crystal

The energy density of Li-ion batteries is closely related to the capacity and average voltage of cathode materials. Unfortunately, current cathode materials either have low capacity or voltage, which limits the development of high-energy-density Li-ion batteries. This has given challenge to many attempts to develop new cathode materials with high capacity and voltage. In this study, we find that Li easily inserts into the (111) plane of SiC in the presence of Si, and a well-organized Li-rich SiC twin crystal is formed. Ultraviolet–visible diffuse reflectance spectra and electrochemical test results suggest that this Li-rich SiC twin crystal possesses the band gap energy of 3.5 eV and charging capacity of 1979 mAh/g at the current density of 200 mA/g, making it a promising candidate for the cathode material in high-capacity Li-ion batteries. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy results reveal that Si-induced Li insertion contributes to the changes in the surface species and structure of pristine SiC. These findings suggest that the Li-rich SiC twin crystal raises new possibilities for the development of high-capacity cathode materials and merits further investigation to expand its application scope.     

Synthesis of layered cathode materials Li[CoxNiyMn1-x-y]O2 from layered double hydroxide precursors

Cathode materials Li[CoxNiyMn1-x-y]O2 for lithium secondary batteries have been prepared by a new route using layered double hydroxides (LDHs) as a precursor. The resulting layered phase with the α-NaFeO2 structure crystallizes in the rhombohedral system, with space group R-3m having an interlayer spacing close to 0.47 nm. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation states of Co, Ni and Mn. The effects of varying the Co/Ni/Mn ratio on both the structure and electrochemical properties of Li[CoxNiyMn1-x-y]O2 have been investigated by X-ray diffraction and electrochemical tests.The products demonstrated a rather stable cycling behavior, with a reversible capacity of 118 mAh/g for the layered material with Co/Ni/Mn = 1/1/1.     

Integrating trace Ti-doping and LiYO2-coating to stabilize Ni-rich cathodes for lithium-ion batteries

Ni-rich layered cathodes have become the promising candidates for the next-generation high-energy Li-ion batteries due to their high energy density and competitive cost. However, they suffer from rapid capacity fading due to the structural and interfacial instability upon long-term operation. Herein, the Ti-doped and LiYO₂-coated Ni-rich layered cathode has been synthesized via a facile one-step sintering strategy, which significantly restrains the interfacial parasitic side reactions and enhances the structural stability. Specifically, the trace Ti⁴⁺ doping greatly stabilizes the lattice oxygen and alleviates the Li/Ni disorder while the LiYO₂ coating layer can prevent the erosion of the cathode by the electrolyte during cycles. As a result, the Ti-NCM83@LYO delivers a high specific capacity of 135 mAh g⁻¹ even at 10C and there is almost no capacity loss at 1C for 100 cycles. This work provides a simple one-step dual-modification strategy to meet the commercial requirements of Ni-rich cathodes.     

Mesoporous composite of LiFePO4 and carbon microspheres as positive-electrode materials for lithium-ion batteries

Mesoporous LiFePO₄/C microspheres consisting of LiFePO₄ nanoparticles are successfully fabricated by an eco-friendly hydrothermal approach combined with high-temperature calcinations using cost-effective LiOH and Fe³⁺ salts as raw materials. In this strategy, pure mesoporous LiFePO₄ microspheres, which are composed of LiFePO₄ nanoparticles, were uniformly coated with carbon (∼1.5 nm). Benefiting from this unique architecture, these mesoporous LiFePO₄/C microspheres can be closely packed, having high tap density. The initial discharge capacity of LiFePO₄/C microspheres as positive-electrode materials for lithium-ion batteries could reach 165.3 mAh/g at 0.1 C rate, which is notably close to the theoretical capacity of LiFePO₄ due to the large BET surface area, which provides for a large electrochemically available surface for the active material and electrolyte. The material also exhibits high rate capability (∼100 mAh/g at 8 C) and good cycling stability (capacity retention of 92.2% after 400 cycles at 8 C rate).     

Electrochemical performance of polygonized carbon nanofibers as anode materials for lithium-ion batteries

Carbon nanofibers with a polygonal cross section (P-CNFs) synthesized using a catalytic chemical vapor deposition (CCVD) technology have been investigated for potential applications in lithium batteries as anode materials. P-CNFs exhibit excellent high-rate capabilities. At a current density as high as 3.7 and 7.4 A/g, P-CNFs can still deliver a reversible capacity of 198.4 and 158.2 mAh/g, respectively. To improve their first coulombic efficiency, carbon-coated P-CNFs were prepared through thermal vapor deposition (TVD) of benzene at 900 °C. The electrochemical results demonstrate that appropriate amount of carbon coating can improve the first coulombic efficiency, the cycling stability and the rate performance of P-CNFs. After carbon coating, P-CNFs gain a weight increase approximately by 103 wt%, with its first coulombic efficiency increasing from 63.1 to 78.4%, and deliver a reversible capacity of 197.4 mAh/g at a current density of 3.7 A/g. After dozens of cycles, there is no significant capacity degradation at both low and high current densities.     

Carbon combustion synthesis of lithium cobalt oxide as cathode material for lithium ion battery

Lithium cobalt oxide (LiCoO2) was synthesized by carbon combustion synthesis (CCS) using carbon as fuel. X-ray diffraction (XRD) and scanning electron microscope (SEM) measurements showed that carbon combustion led to the formation of layered structure of LiCoO2 and the particle size could be controlled by carbon content. For the LiCoO2 sample prepared at 800 ℃ for 2 h, at molar ratio of C/Co= 0.5, the particle-size distribution fell in the narrow range of 3-5 μm. Electrochemical tests indicated this LiCoO2 sample delivered an initial discharge capacity of 148 mAh/g with capacity retention rate higher than 97% after 10 cycles.     

Microwave-assisted polyol synthesis of LiMnPO4/C and its use as a cathode material in lithium-ion batteries

We synthesized LiMnPO₄/C with an ordered olivine structure by using a microwave-assisted polyol process in 2:15 (v/v) water–diethylene glycol mixed solvents at 130 °C for 30 min. We also studied how three surfactants—hexadecyltrimethylammonium bromide, polyvinylpyrrolidone k30 (PVPk30), and polyvinylpyrrolidone k90 (PVPk90)—affected the structure, morphology, and performance of the prepared samples, characterizing them by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, charge/discharge tests, and electrochemical impedance spectroscopy. All the samples prepared with or without surfactant had orthorhombic structures with the Pnmb space group. Surfactant molecules may have acted as crystal-face inhibitors to adjust the oriented growth, morphology, and particle size of LiMnPO₄. The microwave effects could accelerate the reaction and nucleation rates of LiMnPO₄ at a lower reaction temperature. The LiMnPO₄/C sample prepared with PVPk30 exhibited a flaky structure coated with a carbon layer (∼2 nm thick), and it delivered a discharge capacity of 126 mAh/g with a capacity retention ratio of ∼99.9% after 50 cycles at 1C. Even at 5C, this sample still had a high discharge capacity of 110 mAh/g, demonstrating good rate performance and cycle performance. The improved performance of LiMnPO₄ likely came from its nanoflake structure and the thin carbon layer coating its LiMnPO₄ particles. Compared with the conventional polyol method, the microwave-assisted polyol method had a much lower reaction time.     

Carbon combustion synthesis of lithium cobalt oxide as cathode material for lithium ion battery

Lithium cobalt oxide （LiCoO2） was synthesized by carbon combustion synthesis （CCS） using carbon as fuel. X-ray diffraction （XRD） and scanning electron microscope （SEM） measurements showed that carbon combustion led to the formation of layered structure of LiCoO2 and the particle size could be controlled by carbon content. For the LiCoO2 sample prepared at 800℃ for 2 h, at molar ratio of C/Co = 0.5, the particle-size distribution fell in the narrow range of 3-5 μm. Electrochemical tests indicated this LiCoO2 sample delivered an initial discharge capacity of 148 mAh/g with capacity retention rate higher than 97% after 10 cycles.     

Preparation and electrochemical performance of carbon-coated LiFePO4/LiMnPO4-positive material for a Li-ion battery

Lithium iron phosphate (LiFePO₄)/lithium manganese phosphate (LiMnPO₄)-positive material was successfully prepared through ball milling and high-temperature sintering using manganese acetate, lithium hydroxide, ammonium dihydrogen phosphate, and ferrous oxalate as raw materials. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, a constant current charge–discharge test, cyclic voltammetry, and electrochemical impedance spectroscopy. The effects of lithium iron phosphate coating were also discussed. Because of its special core–shell structure, the as-prepared LiMn_0.7Fe_0.3PO₄–LiFePO₄–C exhibits excellent electrochemical performance. The discharge capacity reached 136.6 mAh/g and the specific discharge energy reached 506.9 Wh/kg at a rate of 0.1 C.     

预压下锆基块体非晶合金的热冲击变形与破坏

实验研究了不同预压载荷与加热速率下Zr51Ti5Ni10Cu25Al9块体非晶合金的失效温度和破坏规律, 发现预压力和温升率较低时, 随着温度的升高, 材料强度减小, 样品最后发生塑性变形; 预压力和温升率较高时样品则发生剪切断裂, 且发生剪切破坏时样品的温度高于其玻璃化转变温度.基于变温条件下的结构弛豫模型, 分析了块体非晶合金在快速加热条件下的变形过程,给出了材料发生屈服时的温度与温升率、预压力与屈服温度之间的相互关系, 并得出了实验结果的拟合关系式. 对回收样品断裂面进行分析, 发现了与恒温压缩断裂明显不同的断裂特征. 最后分析了预压载荷下快速加热过程中上述材料发生剪切破坏的临界条件.      

Lithium-storage properties of SiO2 nanotubes@C using carbon nanotubes as templates

Silica-based anode material is the most concerned material at present, which has the advantages of good cycle stability, high theoretical specific capacity and abundant reserves. However, silica suffers from inherent low conductivity, severe volume expansion effect and low initial coulombic efficiency, which limits its application in lithium-ion batteries. Nanotubes structure can mitigate the volume expansion during lithiation/delithiation. In this article, silica nanotubes (SNTs) were prepared using carbon nanotubes (CNTs) as a template, and then the uniform carbon layer was coated on their surface by carbonization of citric acid. The hollow structure of nanotubes provides more sites for the insertion of Li⁺ during lithiation and additional channels for Li⁺ migration in the cycles, which improves the electrochemical performance. Conductivity can be enhanced by coating carbon layer. The specific capacity of the composite material is about 650 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles. With a specific capacity of 400 mAh g⁻¹ even at 1 A g⁻¹ after 100 cycles. The silica-based material is a competitive anode material for lithium-ion batteries.     

Atomic-scale simulations for lithium dendrite growth driven by strain gradient

Dendrite formation is a major obstacle, e.g., capacity loss and short circuit, to the next-generation high-energy-density lithium (Li)-metal batteries. The development of successful Li dendrite mitigation strategies is impeded by an insufficient understanding in Li dendrite growth mechanisms. The Li-plating-induced internal stress in Li-metal and its effects on dendrite growth have been widely studied, but the underlying microcosmic mechanism is elusive. In the present study, the role of the plating-induced stress in dendrite formation is analyzed through first-principles calculations and ab initio molecular dynamic (AIMD) simulations. It is shown that the deposited Li forms a stable atomic nanofilm structure on the copper (Cu) substrate, and the adsorption energy of Li atoms increases from the Li-Cu interface to the deposited Li surface, leading to more aggregated Li atoms at the interface. Compared with the pristine Li-metal, the deposited Li in the early stage becomes compacted and suffers the in-plane compressive stress. Interestingly, there is a giant strain gradient distribution from the Li-Cu interface to the deposited Li surface, making the deposited atoms adjacent to the Cu surface tend to press upwards with perturbation and causing the dendrite growth. This provides an insight into the atomicscale origin of Li dendrite growth, and may be useful for suppressing the Li dendrite in Li-metal-based rechargeable batteries.     

Higher-order polysulfides induced thermal runaway for 1.0 Ah lithium sulfur pouch cells

Comprehensive analyses on thermal runaway mechanisms are critically vital to achieve the safe lithium–sulfur (Li–S) batteries. The reactions between dissolved higher-order polysulfides and Li metal were found to be the origins for the thermal runaway of 1.0 Ah cycled Li–S pouch cells. 16-cycle pouch cell indicates high safety, heating from 30 to 300 °C without thermal runaway, while 16-cycle pouch cell with additional electrolyte undergoes severe thermal runaway at 147.9 °C, demonstrating the key roles of the electrolyte on the thermal safety of batteries. On the contrary, thermal runaway does not occur for 45-cycle pouch cell despite the addition of the electrolyte. It is found that the higher-order polysulfides (Li₂S_x ≥ 6) are discovered in 16-cycle electrolyte while the sulfur species in 45-cycle electrolyte are Li₂S_x ≤ 4. In addition, strong exothermic reactions are discovered between cycled Li and dissolved higher-order polysulfide (Li₂S₆ and Li₂S₈) at 153.0 °C, driving the thermal runaway of cycled Li–S pouch cells. This work uncovers the potential safety risks of Li–S batteries and negative roles of the polysulfide shuttle for Li–S batteries from the safety view.     

Synthesis of layered cathode materials Li[CoxNiyMn1−x−y]O2 from layered double hydroxide precursors

Cathode materials Li[Co_xNi_yMn_1?x?y]O₂ for lithium secondary batteries have been prepared by a new route using layered double hydroxides (LDHs) as a precursor. The resulting layered phase with the α-NaFeO₂ structure crystallizes in the rhombohedral system, with space group R-3m having an interlayer spacing close to 0.47 nm. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation states of Co, Ni and Mn. The effects of varying the Co/Ni/Mn ratio on both the structure and electrochemical properties of Li[Co_xNi_yMn_1?x?y]O₂ have been investigated by X-ray diffraction and electrochemical tests. The products demonstrated a rather stable cycling behavior, with a reversible capacity of 118 mAh/g for the layered material with Co/Ni/Mn = 1/1/1.     

Al2O3基陶瓷刀具材料摩擦磨损特性及其有限元分析

以添加TiC、Ti（C，N）和SiCw 3种Al2O3基陶瓷刀具材料作为研究对象，在MRH-3型高速环-块摩擦磨损试验机上研究3种陶瓷刀具材料在相同试验条件下的摩擦磨损性能，通过扫描电子显微镜对陶瓷的磨损表面进行观察，并利用ANSYS有限元软件分析计算磨损时的应力分布．结果表明，Al2O3基陶瓷刀具材料的摩擦磨损特性与其添加剂的种类有关，其抗磨性能由大到小顺序依次为Al2O3／SiCw〉Al2O3／Ti（C，N）〉Al2O3／TiC．Al2O3基陶瓷刀具的摩擦磨损性能与其硬度（H）、弹性模量（E）和断裂韧性（KIC）有关，磨损率W随E／H增加而增大，随KIC增加而减小．Al2O3／TiC陶瓷刀具材料的磨损机理以粘着磨损为主，Al2O3／Ti（C，N）和Al2O3／SiCw陶瓷刀具材料的磨损机理主要为磨粒磨损．     

Particulate modification of lithium-ion battery anode materials and electrolytes

Lithium-ion batteries (LIBs) are considered a rechargeable and commercial energy storage device for electronic equipment such as smartphone and electric vehicles. Despite the prospective future of LIBs, unsatisfied electrochemical properties like reversible capacity, cycle ability and coulombic efficiency still hinder their development. High volume expansion rate, uncontrolled Li dendrite growth and unsatisfied solid electrolyte interphase also occur when LIBs are applied in long-time usage. Numerous modification methods such as exploring high-capacity anode/cathode materials, constructing artificial solid electrolyte interphase and improved conductive binders can be adopted to enhance the performances. Among them, particulate modification for LIBs anode and electrolytes is receiving tremendous attraction in the recent work. The method is composed of changing the morphology and particle size of the active materials, also introduce nano-size additives to the main structure. This review emphasizes on introducing and discussing the modification in following aspects: particulate modification on carbon group IVA element anodes, introduction of additives like transition metal oxide nanoparticles into anode and electrolyte materials, dissipate the influence of Li dendrite growth and ameliorate the performances of solid electrolyte interface. This review hopes to be denoted for the future development of LIBs with the comprehensive understanding on the particulate modification.     

Microwave-hydrothermal preparation of a graphene/hierarchy structure MnO2 composite for a supercapacitor

Graphene/hierarchy structure manganese dioxide （GN/MnO2） composites were synthesized using a simple microwave-hydrothermal method. The properties of the prepared composites were analyzed using field emission scanning electron microscopy （FE-SEM）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and X-ray photoelectron spectroscopy （XPS） measurements. The electrochemical performances of the composites were analyzed using cyclic voltammetry, electrochemical impedance spectrometry （EIS）, and chronopotentiometry. The results showed that GN/MnO2 （10 wt% graphene） displayed a specific capacitance of 244 F/g at a current density of 100 mA/g. An excellent cyclic stability was obtained with a capacity retention of approximately 94.3% after 500 cycles in a 1 mol/L Li2SO4 solution. The improved electrochemical performance is attributed to the hierarchy structure of the manganese dioxide, which can enlarge the interface between the active materials and the electrolyte. The prepa- ration route provides a new approach for hierarchy structure graphene composites; this work could be readily extended to the preparation of other graphene-based composites with different structures for use in energy storage devices.     

Diffusion induced stresses in buckling battery electrodes

Highly networked nanostructured battery electrode materials offer the possibility of achieving both rapid battery charge–discharge rates and high storage capacity. Recently, lithium ion battery (LIB) electrodes based on a 2-D honeycomb architecture were shown to undergo remarkable and reversible morphological changes during the lithiation process. Charge–discharge rates in 3-D composite electrode have also been shown to benefit from sandwiching the electrolytically active material between highly conductive ion and electron transport pathways to reduce electrical resistance and solid-state diffusion lengths. In the present work we simulate and analyze the observed morphological changes in honeycomb electrodes, with and without the presence of conductive pathways, during the lithiation–delithiation process. Diffusion induced stresses are analyzed for such structures undergoing elastic–plastic deformation during cycling. The results show that such a periodic, nanostructured electrode geometry allows for the presence of buckling-like deformation modes, which effectively reduce the resulting mechanical stresses that lead to electrode failure.