Utilizing the capacity below 0 V to maximize lithium storage of hard carbon anodes

Compared with conventional graphite anode, hard carbons have the potential to make reversible lithium storage below 0 V accessible due to the formation of dendrites is slow. However, under certain conditions of high currents and lithiation depths, the irreversible plated lithium occurs and then results in the capacity losses. Herein, we systematically explore the true reversibility of hard carbon anodes below 0 V. We identify the lithiation boundary parameters that control the reversible capacity of hard carbon anodes. When the boundary capacity is controlled below 400 mAh g⁻¹ with current density below 50 mA g⁻¹, no lithium dendrites are observed during the lithiation process. Compared with the discharge cut-off voltage to 0 V, this boundary provides a nearly twice reversible capacity with the capacity retention of 80% after 172 cycles. The results of characterization and finite element model reveal that the large reversible capacity below 0 V of hard carbon anodes is mainly benefited from the dual effect of lithium intercalation and reversible lithium film. After the lithium intercalation, the over-lithiation induces the quick growth of lithium dendrites, worsening the electrochemical irreversibility. This work enables insights of the potentially low-voltage performance of hard carbons in lithium-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 (∼1.5 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).     

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.     

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.     

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.     

Three-Dimensional Study of Graphite-Composite Electrode Chemo-Mechanical Response using Digital Volume Correlation

A custom built reusable cell for in situ lithiation and mechanical deformation studies while in an X-ray tomograph was demonstrated, and the strain and volume changes of a composite graphite anode were computed from 3D X-ray microcomputed tomography data via Digital Volume Correlation (DVC). The test anode was a composite electrode comprised of a porous compliant matrix, graphite as the Li⁺ host material, 5-μm ZrO₂ marker particles for use with DVC, and active carbon black to enhance electrical conductivity. The composite electrodes were hot-pressed to control their porosity, and in turn the mechanical integrity of the resulting material. This composite anode was included in a half-cell and lithiated in situ while in a tomograph, and intermittent 3D data were collected at different lithiation levels up to full gravimetric capacity. Strain measurements by DVC demonstrated relatively uniform expansion of the freestanding electrode with average normal strains in the three directions varying by 20%, while the internal shear strains were found to be negligible. The average experimental strains were about 75% of the theoretical value, as estimated by the rule of mixtures, which implies that ~25% of the normal strains in graphite, due to lithiation, are accommodated by the surrounding matrix.     

Zr-doped titanium lithium ion sieve and EP-granulated composite: Superb adsorption and recycling performance

Lithium ion sieve (LIS) has attracted great attention due to its high adsorption selectivity towards Li⁺. Herein, a new type of Zr-doped Ti-LIS (HZrTO) was synthesized by a simple calcination method. The adsorption capacity increased from 56.3 mg g⁻¹ (before doping) to 93.2 mg g⁻¹ after doping in LiOH solution (lithium 1.8 g L⁻¹). The adsorption isotherm and adsorption kinetics of HZrTO accord with the Langmuir isotherm and the pseudo-second-order kinetic equation, respectively. Batch experiments showed that HZrTO has good stability and selectivity. In addition, HZrTO was granulated via epoxy resin (E-12), and the obtained granular adsorbent showed good adsorption capacity, excellent stability and high selectivity towards Li⁺.     

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）.     

The effect of roller pressure and share of plant matter in mulching soil cultivation on its density and water content

The aim of this study was to assess the impact of the roller load (with cultivating tools) and doses of plant matter (straw and charlock) mixed with soil on the air and humidity conditions of such soil. The innovation of the research consisted in abandoning the use of Kopecky’s cylinders: the bulk density of mulched soil was determined by measuring its mass and volume, which it obtained in vases before and after the roller work. Capillary infiltration was also carried out for soil in vases.Variable research factors characterizing the roller working conditions in the mulching tillage, were: source/type of plant material cut into 10 cm chopped straw, its share in soil, three ranges of soil water content and vertical unit load on the roller.Increasing the straw dose to 30 Mg^.ha⁻¹ reduces the bulk density from 1.17 to 0.76 g^.cm⁻³, while increasing the dose of charlock to 60 Mg^.ha⁻¹ under these conditions, it reduces the density to 1.03 g^.cm⁻³. At the same time, humidity conditions change: volumetric water content decreases in case of straw from 13.9% to 8.5% and increases in case of charlock to 17.4%. Changes occur also in case of full water capacity.     

Research progress in degradation mechanism of silicon anode materials for lithium-ion batteries

硅负极材料由于具有非常高的理论比容量,使之成为锂离子电池极具前景的负极替代材料,然而,硅负极材料在充放电过程中会发生非常大的体积变形,这会引起活性材料的破坏失效,严重影响其电化学循环性能,成为制约其在锂离子电池领域广泛应用的最大瓶颈,本文介绍了硅负极材料的不同结构形态及其在充放电过程中电化学性能的退化机理,并综述了充放电过程中的力学性能演化、相关理论分析、数值模拟计算等方面的最新国际研究进展,展望了硅负极材料力学失效方面的研究重点,     

Using waste to treat waste: Red mud induced hierarchical porous γ-AlOOH and γ-Al2O3 microspheres as superior Pd support for catalytic reduction of 4-nitrophenol

Toward the imperative treatment of the industrial wastewater containing 4-nitrophenol (4-NP) and industrial solid waste red mud (RM), an innovative approach of “Using waste to treat waste” is developed. Valuable element Al is leached from the RM first, the resultant NaAlO₂ solution is hydrothermally converted to γ-AlOOH hierarchical porous microspheres (RM γ-AlOOH HPMSs, average diameter: 2.0 μm, S_BET: 77.81 m² g⁻¹, pore volume: 0.38 cm³ g⁻¹) in the presence of urea. The subsequent mild thermal conversion results in γ-Al₂O₃ hierarchical porous microspheres (RM γ-Al₂O₃ HPMSs). Both of the RM γ-AlOOH and RM γ-Al₂O₃ HPMSs are employed as the Pd catalyst support for the catalytic reduction of 4-NP. Particularly, the as-obtained composite Pd/RM γ-AlOOH and Pd/RM γ-Al₂O₃ exhibit excellent catalytic activities with superior k_nor as 8204.5 and 4831.4 s⁻¹ g⁻¹, respectively, significantly higher than that of most Pd based catalysts. Moreover, the excellent catalytic stability and durability of the Pd/RM γ-AlOOH and Pd/RM γ-Al₂O₃ within 10 successive cycles of reduction enable the present industrial solid waste RM induced γ-AlOOH and γ-Al₂O₃ HPMSs as great promising Pd catalyst support for the reduction of the industrial wastewater containing 4-NP.     

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.     

Composing atomic transition metal sites for high-performance bifunctional oxygen electrocatalysis in rechargeable zinc–air batteries

Rechargeable zinc–air batteries have attracted extensive attention as clean, safe, and high-efficient energy storage devices. However, the oxygen redox reactions at cathode are highly sluggish in kinetics and severely limit the actual battery performance. Atomic transition metal sites demonstrate high electrocatalytic activity towards respective oxygen reduction and evolution, while high bifunctional electrocatalytic activity is seldomly achieved. Herein a strategy of composing atomic transition metal sites is proposed to fabricate high active bifunctional oxygen electrocatalysts and high-performance rechargeable zinc–air batteries. Concretely, atomic Fe and Ni sites are composed based on their respective high electrocatalytic activity on oxygen reduction and evolution. The composite electrocatalyst demonstrates high bifunctional electrocatalytic activity (ΔE = 0.72 V) and exceeds noble-metal-based Pt/C + Ir/C (ΔE = 0.79 V). Accordingly, rechargeable zinc–air batteries with the composite electrocatalyst realize over 100 stable cycles at 25 mA cm⁻². This work affords an effective strategy to fabricate bifunctional oxygen electrocatalysts for high-performance rechargeable zinc–air batteries.     

Influences of ions and temperature on performance of carbon nano-particulates in supercapacitors with neutral aqueous electrolytes

A commercial product of carbon nano-particles, Cabot MONACH 1300 pigment black (CMPB), was studied for basic structural information and electrochemical performance in neutral aqueous electrolytes, aiming at applications in supercapacitors. As confirmed by SEM and HRTEM, the CMPB had a hierarchical structure, containing basic 10 nm nano-spheres which combined into ca. 50 nm agglomerates which further aggregated into larger particles of micrometres. The capacitance of this commercial material was found to increase with decreasing the size of hydrous cation (Li⁺ → Na⁺ → K⁺), instead of the cation crystal radius (K⁺ → Na⁺ → Li⁺) when coupled with the same anion (Cl⁻). In electrolytes with the same cation concentration (K⁺), changing the anion from the larger dianion (SO₄²⁻) to the smaller monoanion (Cl⁻) also increased the capacitance at high potential scan rates (>50 mV/s). Increasing electrolyte concentration produced expected effect, including raising the electrode capacitance, but lowering the equivalent series resistance (ESR), charge transfer resistance (CTR), and the diffusion resistance. At higher temperatures, the CMPB exhibited slightly higher capacitance, which does not agree with the Gouy–Chapman theory on electric double layer (EDL). A hypothesis is proposed to account for the capacitance increase with temperature as a result of the CMPB opening up some micro-pores for more ions to access in response to the temperature increase.     

Preparation and Li+ storage properties of hierarchical hollow porous carbon spheres

Hollow ordered porous carbon spheres (HOPCS) with a hierarchical structure were prepared by templating with hollow ordered mesoporous silica spheres (HOMSS). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that HOPCS exhibited a spherical hollow morphology. High-resolution TEM, small angle X-ray diffraction (SAXRD) and N₂ sorption measurements confirmed that HOPCS inversely replicated the unconnected hexagonal-stacked pore structure of HOMSS, and possessed ordered porosity. HOPCS exhibited a higher storage capacity for Li⁺ ion battery (LIB) of 527.6 mA h/g, and good cycling performance. A large capacity loss during the first discharge–charge cycle was found attributed to the high content of micropores. The cycling performance was derived from the hierarchical structure.     

Microfluidic platform serves as controllable fabrication of binary Mo/Ir nanodots/carbon hetero-material for efficient electrocatalytic nitrogen reduction

Electrocatalytic nitrogen reduction reaction (NRR) is regarded as a potential routine to achieve environment-friendly ammonia production, because of its abundant nitrogen resources, clean energy utilization and flexible operation. However, it is hindered by low activity and selectivity, in which condition well-designed catalysts are urgently in need. In this work, a binary Mo/Ir nanodots/carbon (Mo/Ir/C) hetero-material is efficiently constructed via microfluidic strategy, of which the nanodots are homogeneously distributed on the carbon skeleton and the average size is approximately 1 nm. Excellent performance for NRR is obtained in 1 mol L⁻¹ KOH, of which the optimized ammonia yield and faradic efficiency are 7.27 μg h⁻¹ cm⁻² and 2.31% respectively. Moreover, the optimized ammonia yield of 6.20 μg h⁻¹ cm⁻² and faradic efficiency of 10.59% are also obtained in 0.005 mol L⁻¹ H₂SO₄. This work achieves the continuous-flow synthesis and controllable adjustment of hetero-materials for favorable morphologies, which provides an innovative pathway for catalyst design and further promotes the development of ammonia production field.     

Preparation of bunched CeO2 and study on microwave absorbing properties with MWCNTs binary composite

A novel bunched cerium oxide (CeO₂) was prepared and its binary composite material with multi-walled carbon nanotubes presented an excellent microwave absorbing properties. The morphology, structure, and absorbing properties of the composite material were investigated. It was found that the minimum reflection loss (RL) of the composite material at 15.79 GHz was −45.7 dB when the thickness was 5.5 mm. It was worth noting that when the composite material was in the thickness range of 5.0–7.5 mm and the frequency was 11.36–17.77 GHz, the electromagnetic wave RL was < −30 dB, which illustrated that the composite material had a good absorbing effect over a wide thickness range. The results of the study contributed to the design and preparation of efficient microwave absorbing materials (MAM) with rare earth oxide composites and their applications, which demonstrated the importance of new composites with special structures in the field of MAM.     

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.     

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.     

Lithiation-enhanced charge transfer and sliding strength at the silicon-graphene interface:A first-principles study

The application of silicon as ultrahigh capacity electrodes in lithium-ion batteries has been limited by a number of mechanical degradation mechanisms including fracture, delamination and plastic ratcheting, as a result of its large volumetric change during lithiation and delithiation. Graphene coating is one feasible technique to mitigate the mechanical degradation of Si anode and improve its conductivity. In this paper, first-principles calculations are performed to study the atomic structure, charge transfer and sliding strength of the interface between lithiated silicon and graphene. Our results show that Li atoms segregate at the(lithiated) Si-graphene interface preferentially, donating electrons to graphene and enhancing the interfacial sliding resistance. Moreover, the interfacial cohesion and sliding strength can be further enhanced by introducing single-vacancy defects into graphene.These findings provide insights that can guide the design of stable and efficient anodes of silicon/graphene hybrids for energy storage applications.