Synthesis of LiNi0.8Co0.2O2 cathode material through sintering in an air environment and electrochemical properties characterization

制备锂离子电池正极材料LiNi_0.8Co_0.2O₂通常需要在纯氧气气氛下进行烧结.本工作以硫酸镍,硫酸钴和氢氧化钠为原料,采用并流共沉淀法制备了高密度Ni_0.8Co_0.2(OH)₂前驱体,再采用高温固相反应法在空气中烧结制备了锂离子电池LiNi_0.8Co_0.2O₂正极材料.采用X射线衍射(XRD),扫描电镜(SEM),恒流充放电测试(ECT),循环伏安(CV)与比表面积(BET)测试等方法对目标样品进行了表征,详细考察了烧结条件对材料结构,微观形貌及电化学性能的影响.结果表明,锂/(钴+镍)摩尔比为1.13∶1时,在管式炉中和空气气氛下于第一段烧结温度700 ℃保温9 h,于第二段烧结温度750 ℃保温12 h,合成的材料比表面积适中(0.78 m²/g),具有规则的六边形α-NaFeO₂层状结构,晶粒分布均匀,电化学性能最优.在0.5 C充放电倍率下和2.7~4.3 V电压范围内,其首次放电比容量达到153.0 mA·h/g,循环20次后放电比容量仍为150.7 mA·h/g,容量保持率达到98.5%,显示了优异的循环稳定性能,可用做高能量密度动力电池正极材料.     

A more economical choice for the cathode material of Ni-MH batteries with high electrochemical performances: 3D flower-like Ni–Fe LDHs

A series of 3D flower-like Ni–Fe layered double hydroxides (LDHs) were synthesized successfully and used as the cathode materials for nickel-metal hydride battery (Ni-MH battery). The 4Ni–Fe LDH electrode (Ni/Fe molar ratio = 4:1) displays the highest high-rate discharge property and the most excellent cycling performance. The discharge capacity of the 4Ni–Fe LDH electrode can reach up to 291.3 mAh/g at a discharge rate of 200 mA/g and which delivers a high capacity retention of 98.9% over 200 cycles. In contrast, the pure Ni(OH)₂ electrode only has a capacity of 243 mAh/g, and after 100 cycles the capacity retention is just 73.4%. The above improvement can be ascribed to the formation of Ni–Fe LDHs which can consolidate the stability of α-Ni(OH)₂ in the KOH solution. In addition, the unique flower-like morphology and the enlarged interlayer spacing also paly important role to promote ion transmission and charge transfer. Considering the competitive price of Fe, 3D flower-like Ni–Fe LDH may be a more economical choice for the cathode material of Ni-MH batteries.     

Synthesis and characterization of submicron-sized LiNi1/3Co1/3Mn1/3O2 by a simple self-propagating solid-state metathesis method

Submicron-sized LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials were synthesized using a simple self-propagating solid-state metathesis method with the help of ball milling and the following calcination. A mixture of Li(ac)·2H₂O, Ni(ac)₂·4H₂O, Co(ac)₂·4H₂O, Mn(ac)₂·4H₂O (ac = acetate) and excess H₂C₂O₄·2H₂O was used as starting material without any solvent. XRD analyses indicate that the LiNi_1/3Co_1/3Mn_1/3O₂ materials were formed with typical hexagonal structure. The FESEM images show that the primary particle size of the LiNi_1/3Co_1/3Mn_1/3O₂ materials gradually increases from about 100 nm at 700 °C to 200–500 nm at 950 °C with increasing calcination temperature. Among the synthesized materials, the LiNi_1/3Co_1/3Mn_1/3O₂ material calcined at 900 °C exhibits excellent electrochemical performance. The steady discharge capacities of the material cycled at 1 C (160 mA g⁻¹) rate are at about 140 mAh g⁻¹ after 100 cycles in the voltage range 3–4.5 V (versus Li⁺/Li) and the capacity retention is about 87% at the 350th cycle.     

A quinary high entropy metal oxide exhibiting robust and efficient bidirectional O2 reduction and water oxidation

The O₂/H₂O couple-based transformation between renewable energy and electricity has emerged as a key step in implementing a carbon-neutral energy infrastructure. Therefore, an inexpensive and efficient electrocatalyst driving both O₂ reduction and O₂ evolution reaction in water becomes critical that can be directly applied in a unitized regenerative fuel cell in both electrolyzer or fuel cell mode. Here, we have crafted a high entropy metal oxide (HEO) containing readily abundant first-row transition metals (Fe, Cr, Co, Mn, Ni) via a metal-organic framework intermediate followed by regulated annealing at 750 °C. This material exhibited bidirectional ORR and OER activity in alkaline aqueous media (pH 14.0) with excellent energy efficiency on either side, showcasing a difference of 0.79 V (while achieving 10 mA cm⁻² current density) and ∼90% Faradaic efficiency. The in-depth electrochemical and surface analysis pointed out the key formation of the Ni–OOH layer on the HEO particle and the optimal porosity for maximized electrochemical surface area generation as pivotal factors behind its superior reactivity. An alkaline electrolyzer was assembled with this HEO (anode) and Ni-foam (cathode), which demonstrated concurrent production of O₂ and H₂ over 6 h with minimal alterations in the anodic material. Therefore, this robust, inexpensive, and scalable HEO material can boost the progress in developing sustainable electrolyzer/fuel cell assemblies.     

Preparation and characterization of layered LiMn1/3Ni1/3Co1/3O2 as a cathode material by an oxalate co-precipitation method

The layered LiMn_1/3Ni_1/3Co_1/3O₂ cathode materials were synthesized by an oxalate co-precipitation method using different starting materials of LiOH, LiNO₃, [Mn_1/3Ni_1/3Co_1/3]C₂O₄·2H₂O and [Mn_1/3Ni_1/3Co_1/3]₃O₄. The morphology, structural and electrochemical behavior were characterized by means of SEM, X-ray diffraction analysis and electrochemical charge–discharge test. The cathode material synthesized by using LiNO₃ and [Mn_1/3Ni_1/3Co_1/3]C₂O₄·2H₂O showed higher structural integrity and higher reversible capacity of 178.6 mAh g⁻¹ in the voltage range 3.0–4.5 V versus Li with constant current density of 40 mA g⁻¹ as well as lower irreversible capacity loss of 12.9% at initial cycle. The rate capability of the cathode was strongly influenced by particle size and specific surface area.     

High performance hybrid supercapacitors with LiNi1/3Mn1/3Co1/3O2/activated carbon cathode and activated carbon anode

Hybrid supercapacitors have been studied as a next generation energy storage device that combines the advantages of supercapacitors and batteries. One important challenge of hybrid supercapacitors is to improve energy density (8.9–42 Wh/kg) with maintaining excellent power density (800–7989 W/kg) and cyclability (98.9% after 9000 cycles). Herein, we demonstrate an approach to design hybrid supercapacitors based on LiNi_1/3Mn_1/3Co_1/3O₂ (NMC)/activated carbon (AC) cathode and AC anode (NMC/AC//AC). The NMC/AC//AC hybrid supercapacitors shows outstanding electrochemical performances due to the enhanced energy and power densities. These findings suggest that the NMC/AC cathode is an effective method for high performance hybrid supercapacitors.     

Construction of Li-ion supercapacitor-type battery using active carbon/LiNi0.5Co0.2Mn0.3O2 composite as cathode and its electrochemical performances

采用有机体系（NMP+PVDF）混料及乙醇萃取的方法成功制得活性炭/LiNi_0.5Co_0.2Mn_0.3O₂（AC/NCM）复合电极片,通过设计不同AC/NCM配比能够调控能量和功率密度。选取AC/NCM为1/3配比的复合正极和硬碳（HC）负极组装的超级电容电池循环伏安（CV）曲线呈现近似矩形的容性特征,恒流充放电过程电压随时间的变化（V-t曲线）呈现出良好的线性行为。此外,采用导电炭黑（SP）/碳纳米管（CNT）/石墨烯（graphene）=3/1/1的质量比设计了复合导电剂,立体导电网络的构建有效降低了器件内阻。按照IEC 62660—1标准,在2.5～4.2 V电压窗口,83.4 W/kg功率密度下测得的能量密度高达66.6 W·h/kg,在最大功率密度6.5 kW/kg下测得的能量密度为21.5 W·h/kg。器件充满电后在65℃高温存储168 h能量保有率为97.4%,且无任何胀气现象,平均自放电率为27.5 mV/天,表现出优良的高温特性。采用14 C和50 C电流循环充放电1000次后能量保有率分别为99.06%和96.45%,体现出该超级电容电池的长寿命优势。在12 kW/kg平均放电功率密度下进行脉冲测试,连续放电100次后该器件仍表现出良好的稳定性,表明在车辆启动、脉冲器件等领域具有极大的应用潜力。     

Graphite modified LiNi1/3Co1/3Mn1/3O2 cathodes with improved performance for lithium-ion battery

通过丝网印刷方法用石墨改性LiNi_1/3Co_1/3Mn_1/3O₂（NCM）电极片的表面。采用X射线衍射（XRD）和扫描电子显微镜（SEM）表征未改性和改性电极片的晶体结构和形貌特征,恒流充放电测试评估两种样品的电池性能,CV和EIS测试比较两种样品的电化学极化程度。结果表明,改性NCM电极的晶体结构没有明显变化;在改性电极片的表面上检测到了片状石墨;在截止电压为4.3 V的条件下改性样品比未改性样品具有更好的循环性能和倍率性能;石墨印刷的样品可以减缓电化学极化的增加。     

A highly active composite electrocatalyst Ni–Fe–P–Nb2O5/NF for overall water splitting

This work demonstrates a facile Nb₂O₅-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb₂O₅/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm^?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb₂O₅/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm^?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm^?2).     

LiNi1/3Co1/3Mn1/3O2/polypyrrole composites as cathode materials for high-performance lithium-ion batteries

Polypyrrole is successfully introduced to enhance the reaction stability and ionic conductivity of LiNi_1/3Co_1/3Mn_1/3O₂ material through an ultrasound dispersion method and applied as cathode materials for lithium-ion batteries. This polymer can significantly advance the electrochemical properties. Expectedly, the 8 wt.% LiNi_1/3Co_1/3Mn_1/3O₂/polypyrrole composite has lower mixing degree of Li⁺/Ni²⁺, higher c/a value, which delivers the first discharge capacity of 199.2 mAh g⁻¹, which abate to 121.3 mAh g⁻¹ in the 300th cycle at 0.2 C between 2.5 and 4.5 V. Even at 3 C, it continues to reveal a reversible capacity of 86.4 mAh g⁻¹ after 100 cycles. All the consequences implied that the 8 wt.% LiNi_1/3Co_1/3Mn_1/3O₂/polypyrrole verified a minor charge transfer resistance and better Li⁺ diffusion ability, hence establishing preferable rate and cycling performance compared with the primordial LiNi_1/3Co_1/3Mn_1/3O₂.     

Li(Ni1/3Co1/3Mn1/3)O2 as a suitable cathode for high power applications

The electrochemical performance of the layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ material have been investigated as a promising cathode for a hybrid electric vehicle (HEV) application. A C/Li(Ni_1/3Co_1/3Mn_1/3)O₂ cell, cycled between 2.9 and 4.1 V at 1.5 C rate, does not show any sign of capacity fade up to 100 cycles, whereas at the 5 C rate, a loss of only 18% of capacity is observed after 200 cycles. The Li(Ni_1/3Co_1/3Mn_1/3)O₂ host cathode converts from the hexagonal to a monoclinic symmetry at a high state of charge. The cell pulse power capability on charge and discharge were found to exceed the requirement for powering a hybrid HEV. The accelerated calendar life tests performed on C/Li(Ni_1/3Co_1/3Mn_1/3)O₂ cells charged at 4.1 V and stored at 50 °C have shown a limited area specific impedance (ASI) increase unlike C/Li(Ni_0.8Co_0.2)O₂ based-cells. A differential scanning calorimetry (DSC) comparative study clearly showed that the thermal stability of Li(Ni_1/3Co_1/3Mn_1/3)O₂ is much better than that of Li(Ni_0.8Co_0.2)O₂ and Li(Ni_0.8Co_0.15Al_0.05)O₂ cathodes. Also, DSC data of Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode charged at 4.1, 4.3, and 4.6 V are presented and their corresponding exothermic heat flow peaks are discussed.     

Three-dimensional porous Mn–Ni/Al2O3 microspheres for enhanced low temperature CO hydrogenation to produce methane

CO methanation has attracted much attention because it transforms CO in syngas and coke oven gas into CH₄. Here, porous Al₂O₃ microspheres were successfully used as catalyst supports meanwhile the Mn was used as a promoter of Ni/Al₂O₃ catalysts. The as-obtained Ni/Al₂O₃ and Mn–Ni/Al₂O₃ samples display a micro-spherical morphology with a center diameter near 10 μm. Versus the Ni/Al₂O₃ catalyst, the 10Mn–Ni/Al₂O₃ catalyst exhibits a high specific surface area of 92.5 m²/g with an average pore size of 7.0 nm. The 10Mn–Ni/Al₂O₃ catalyst has the best performance along with can achieve a CO conversion of 100% and a CH₄ selectivity of 90.7% at 300 °C. Even at 130 °C, the 10Mn–Ni/Al₂O₃ catalyst shows a CO conversion of 44.0% and a CH₄ selectivity of 84.1%. The higher low-temperature catalytic activity may be since the catalyst surface contains more CO adsorption sites and thus has a stronger adsorption performance for CO. Density functional theory (DFT) calculations confirm that the Mn additive enhances the adsorption of CO, especially for the 10Mn–Ni/Al₂O₃ catalyst with the strongest adsorption energy.     

Construction of ZIF-67/MIL-88(Fe,Ni) catalysts as a novel platform for efficient overall water splitting

Constructing bifunctional non-precious metal electrocatalysts is necessary for effective overall water splitting (OWS), but challenging. Herein, a novel hybrid nanostructure of ZIF-67/MIL-88(Fe, Ni), denoted as Co-M-Fe/Ni(x) (x represents the mass of ZIF-67), was successfully synthesized by hydrothermal and in-situ growth method, and showed a highly efficient and stable bifunctionality of both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolyte. The Co-M-Fe/Ni(150) exhibited excellent OER performance with a low overpotential of 269 mV and 149 mV @ 10 mA cm^?2 for OER and HER in 1 mol L^?1 KOH, respectively. With Co-M-Fe/Ni(150) as cathode and anode, the integrated OWS device had achieved low potential of 1.52 V @ 10 mA cm^?2, exhibiting its excellent performance of OWS. Based on the results of experiments, ZIF-67 and MIL-88(Fe, Ni), as metal-organic frameworks (MOFs), which have a large specific surface area, uniform distribution of porous structures facilitates charge transmission, promoting the penetration of electrolytes, and improves electron transfer rate. The mechanism of the superior electrocatalytic performance of Co-M-Fe/Ni(150) may be attributed to the synergy of ZIF-67 and MIL-88(Fe, Ni). This work provides guidance for the rational design or optimization of non-noble composites for energy conversion.     

Enhanced electrochemical properties of LiNi1/3Co1/3Mn1/3O2 cathode material by coating with LiAlO2 nanoparticles

Surface coating of LiNi_1/3Co_1/3Mn_1/3O₂ with LiAlO₂ nanoparticles has been attempted to improve the electrochemical properties of these materials as cathodes in lithuim-ion batteries. The coating is undertaken by a sol–gel method that uses C₉H₂₁O₃Al, LiOH·H₂O and LiNi_1/3Co_1/3Mn_1/3O₂. X-ray diffraction analysis shows that the LiAlO₂ is composed of both α- and β-LiAlO₂ phases. The average size of the particles is about 15 nm. The structure of LiNi_1/3Co_1/3Mn_1/3O₂ is not affected by the LiAlO₂ nanoparticle coating. A 3 wt.% LiAlO₂-coating increases the specific discharge capacity, provides excellent cycling performance (i.e. 96.7% capacity retention after 50 cycles at the 1 C rate) and improves the rate capability. By contrast, heavier coatings (5 wt.%) on LiNi_1/3Co_1/3Mn_1/3O₂ dramatically decrease both the discharge capacity and the rate capability, but enhance the cycle life.     

Investigation of LiNi1/3Co1/3Mn1/3O2 cathode particles after 300 discharge/charge cycling in a lithium-ion battery by analytical TEM

Using analytical transmission electron microscopy (TEM) techniques reveal a zigzag layer on surface of the cycled particles of LiNi_1/3Co_1/3Mn_1/3O₂ cathode after 300 discharge/charge cycles. The Ni, Mn content in the zigzag layer of the cycled particle has decreased rapidly from interior to edge of the zigzag layer of the cycled particles. The structure of LiNi_1/3Co_1/3Mn_1/3O₂ oxide was gradually destructed from hexagonal cell with P3₁12 at interior region to fcc lattice of α-NaFeO₂ at edge of the zigzag layer of the cycled particles. These experimental data provide the compositional and structural origins of the capacity decrease in the Li-ion battery.     

Effect of CaCO3 addition on the electrochemical generation of syngas from CO2/H2O in molten salts

A novel green method was presented for the simultaneous synthesis of syngas, a mixture of CO and H₂, via the co-electrolysis of CO₂/H₂O using an established eutectic-salt electrolyte. Optimum electrolysis was carried out at 2.2 V using a two-electrode system composed of a coiled Fe cathode and a coiled Ni anode in eutectic Li_1.07Na_0.75Ca_0.045CO₃/0.15LiOH. The molar ratio of H₂/CO was finely tuned from 1.96 to 7.97 by controlling the amount of CaCO₃. The optimized current efficiency, ～92%, was acquired by 14.28 wt% CaCO₃ addition. Moreover, the relatively low operating temperature of 600 °C was beneficial for practical applications compared to previously reported temperatures in excess of 800 °C, providing a feasible basis for syngas production via electrochemical synthesis. In this manner, CO₂/H₂O was synergistically converted into valuable chemicals, allowing the CO₂ to be utilized efficiently for the conversion and storage of electricity to chemical energy.     

Towards a high performing lithium polymer battery system (VARTA PoLiFlex™)

The design of a lithium polymer battery with excellent properties is presented. The focus is on cathode and anode active materials and their influence on cell properties like energy density and cycle behavior. Standard LiCoO₂ is compared with alternative cathode materials like Li–Co–Ni–Mn–O and high density LiCoO₂. Furthermore, several natural graphites and their mixtures with synthetic graphite are discussed as potential anode active material as natural graphite is attractive concerning price. The good performance of VARTA Microbattery's PoLiFlex™ lithium polymer battery results from an adequate combination of cathode and anode formulations.     

High power BaFe(VI)O4/MnO2 composite cathode alkaline super-iron batteries

This short communication demonstrates that not only pure Fe(VI) cathodes, but also MnO₂/Fe(VI) composite cathodes can substantially enhance the high power discharge of alkaline batteries. The 2.8 Ω and 0.7 W high power discharge of alkaline cells are investigated for 3:1 and 1:1 composite MnO₂/BaFeO₄ cathode cells, provide discharge energies intermediate to that found in the (non-composite) BaFeO₄ cathode cell. At a constant 2.8 Ω load, the 1:1 composite MnO₂/BaFeO₄ cell delivers up to 40% higher energy capacity than the MnO₂ pure cathode alkaline cell, and up to three-fold the capacity of the constant 0.7 W power MnO₂ discharge.     

Synthesis and electrochemical properties of multi-doped LiFePO4/C prepared from the steel slag

The paper presents and discusses a novel route to synthesize a multi-doped LiFePO₄/C composite by using steel slag as a raw material. A ferroalloy with suitable molar ratio of Fe, Mn, V, and Cr is recovered from the slag by a selective carbothermic method, and successfully used as source materials of Fe and multiple dopants for preparing the multi-doped LiFePO₄/C. XRD and Rietveld-refined results show that the multi-doped LiFePO₄/C is single olivine-type phase and well crystallized, Mn, V, and Cr atoms occupy Fe site. Elemental mapping image confirms that the elements (Fe, P, Mn, V, and Cr) distribute homogeneously in particles of the multi-doped LiFePO₄/C. The electrochemical performance of prepared cathode was evaluated by galvanostatic charge/discharge and cyclic voltammogram tests. Compared to the undoped LiFePO₄/C prepared only by chemical reagents, the multi-doped LiFePO₄/C exhibits lesser capacity drops with increasing of charge/discharge current density due to the improvement of the electrode reactivity by multi-doping. The results suggest that steel slag is an abundant and inexpensive source materials of iron and dopants for preparing multi-doped LiFePO₄/C.