The leaching process and kinetic behavior of lepidolite in hydrochloric acid were explored systematically. The influence of leaching conditions on the leaching efficiency of valuable metals in lepidolite was investigated. Under optimized conditions, the leaching efficiencies of Li, K, Rb, Cs and Al are 92.02%, 93.31%, 88.59%, 86.75% and 81.07%, respectively. Kinetics research results show that the leaching process conforms to the shrinking core model that is under the mixed control of chemical reaction and diffusion through the solid product layer. In addition, the contribution of solid product layer diffusion to the leaching gradually expands as the temperature rises, but it is still significantly less than the contribution of chemical reaction. Cost saving in the neutralizing agent and leaching processes makes hydrochloric acid an economical leaching agent for lepidolite. Finally, the Li2CO3 product with a purity of 99.89% was synthesized from the hydrochloric acid leachate.

Bimetallic sulfide NiCo2S4 exhibits charming electrochemical energy storage behavior compared with the corresponding nickel cobalt double layered hydroxide, showing abroad application prospects as one kind of electrode materials for supercapacitors. However, up till now, the electrodeposition of NiCo2S4 in sulfate-based electrolyte solution containing thiourea (TU) has not been realized yet. Here, the sulphuration mechanism of the electrodeposition of nickel cobalt sulfide has been studied by controlling the TU dosage. The results indicate that high vulcanization degree can only be achieved by sufficient TU addition because of the complex adsorption and chelation behaviors of TU molecules. The NiCo2S200/NF electrode which is acquired when n(NiSO4): n(CoSO4): n(TU)=1: 2: 200 shows evident boosting of the rate and cyclic capabilities owing to its highest vulcanization degree. In detail, as increasing the current density from 1 to 10 A g-1, a 105.8% capacitance retention (955 F g-1 at 1 A g-1 and 1052.9 F g-1at 10 A g-1) is achieved, exhibiting excellent rate performance. Moreover, after 2000 charge-discharge cycles at 5 A g-1 the discharge specific capacitance keeps 98% of its initial value, demonstrating good cyclic stability. This work provides a new insight into the vulcanization mechanism of NiCo2S4 in sulfate-based nickel cobalt salts solution under electric field.

Development of binder-free electrode of pseudocapacitive material with excellent cycling stability for supercapacitor shows great attraction in energy storage market. Here, nickel cobalt sulfide (NCS) has been successfully grown on carbon cloth (CC) by electrodeposition in a sulfate-based electrolyte solution with thiourea (TU) as sulfur source and chelation agent. The results show that the chemical composition, microstructure and electrochemical performance of the as-prepared electrode can be modulated by tunning the deposition overpotential. The oriented growth of NCS nanosheets driven by electric field coupled with thiourea adsorption endows the deposits with intersected porous nanosheet-array microstructures, which enables the fast electronic and ionic transmissions. The optimal electrode prepared under -1.0 V (vs Ag/AgCl) (denoted as NC2S200-1.0/CC) can deliver a discharge specific capacitance of 909.5 F g- 1 at 1 A g- 1, which can maintain 89.2 % at 10 A g- 1, demonstrating outstanding rate performance. As successively charging and discharging for 4000 cycles at 5 A g- 1, 120.6 % of the initial value can be retained, illustrating exceptional cyclic stability. In addition, the assembled NC2S200-1.0/CC//AC asymmetric supercapacitor can exhibit an energy density of 26.2 Wh kg- 1 which corresponds to a power density of 821.1 W kg- 1, when charging-discharging at 2 A g- 1 for 10000 cycles, a capacitance retention of 75.5 % can be achieved, manifesting good cycling stability. This work provides a new idea for fabricating transition metal sulfides supported binder-free electrode by electrodeposition.

Design of binder-free electrode with high comprehensive performance exhibits great glamour for energy storage devices in recent years. Herein, nickel cobalt layered double hydroxide (NiCo LDH) has been in situ grown on carbon fiber paper (CFP) by an electrochemical route. Thanks to the porous nanosheet-like morphology of the deposited active material, high conductivity of carbon fibers, as well as the strong connection between the deposits and substrate, the optimized electrode, labeled as NiCo LDH-2/CFP (electrodeposited under -1.0 V) can deliver a discharge specific capacitance of 878.4 F g -1 at 1 A g -1 , which can increase to 1068.5 F g -1 at 10 A g -1 , exhibiting excellent rate performance. Moreover, after cycled at 5 A g -1 for 5000 cycles, the capacitance retention can retain 96.1%, revealing unique cyclic stability. This work opens a new window for preparing high performance binder-fee electrodes for supercapacitors, lithium batteries and catalytes.

3D hierarchical structure ZnSe/C improves cycle life of sodium-ion batteries. Zn–O–C bonds served as electron/charge bridge accelerate charge/ion transfer and fast reaction kinetics.

Transition metal selenides have attracted extensive attention for sodium-ion batteries (SIBs) by virtue of high capacity and intrinsic safety. However, mono-metallic selenides suffer from the low conductivity and sluggish kinetics for Na+ ions transfer. Herein, bimetallic selenide (CuSe/ZnSe@NC) is constructed with modified band structure to boost the fast Na+ ions diffusion. Particularly, the implantation of heterojunction triggers the sub-lattice distortion and charge redistribution, which is beneficial to provide abundant active sites and regulate band structure. As expected, bimetallic CuSe/ZnSe@NC delivers the specific capacities of 411.5 mA h g(-1) after 1000 cycles at 1 A g(-1) and 361.8 mA h g(-1) at 5 A g(-1), indicating the superior cycle and rate performance than that of mono-metallic selenides. Meanwhile, in-situ XRD, TEM, and EIS further reveal the high reversibility and the conversion and alloying mechanisms of bimetallic CuSe/ZnSe@NC for SIBs. Moreover, first-principles cal-culations (DFT) further confirm that the fast Na+ ions diffusion is attributed to the optimized band structure and the charge rearrangement. Therefore, bimetallic heterojunctions not only combined the multifunctional prop-erties, but also exhibited unique physicochemical properties that transcend mono-metallic selenides.

Decreasing the particle size of Li2CO3 powder is beneficial for advancing its applications in the manufacturing of different materials and drug delivery. Therefore, in this study, a novel bottom-up process based on freezing is proposed for the production of nanoparticles. Herein, two methods of explosive nucleation were used: addition of an anti-solvent and rapid freezing. Explosive nucleation of Li2CO3 occurred during the initial stage of anti-solvent addition; in contrast, in the freezing method, it occurred at a stage when the solute, which had not migrated, was extruded to the solid-liquid interface. Li2CO3 concentration had an effect on both the crystal grain and particle size. The controlled preparation of Li2CO3 nanoparticles was achieved within a certain range of A/B ratio; when the ratio decreased from 10/0 to 10/20 v/v, the controlled synthesis of Li2CO3 nanoparticles was achieved. A lower concentration of Li2CO3 decreased the size of the crystal grain and increased the size of the particles, as observed via transmission electron microscopy and dynamic light scattering. When the A/B ratio (where A is saturated Li2CO3 solution and B is deionised water) was decreased below 10/20 v/v, the crystal grain size of Li2CO3 did not reduce significantly. To further understand the nucleation, freezing was carried out at two temperatures, i.e. 223 +/- 2 K and 267 +/- 2 K. The lower freezing temperature resulted in a smaller crystal grain size and more concentrated distribution.

By using a combinatorial multi-element co-doping strategy, Ti/Mg/La were doped in Al-doped Co3O4 during the solid-phase sintering process, and the electrochemical performances of the developed LCO-D under high voltage were highly improved.

The addition of 0.5 wt.% of DMTMSP to the electrolyte could improve the low-temperature discharge and cycling performances of high voltage layered lithium cobaltate-based lithium ion batteries.

In recent years, various attempts have been made to meet the increasing demand for high energy density of lithium-ion batteries (LIBs). The increase in voltage can improve the capacity and the voltage platform performance of the electrode materials. However, as the charging voltage increases, the stabilization of the interface between the cathode material and the electrolyte will decrease, causing side reactions on both sides during the charge–discharge cycling, which seriously affects the high-temperature storage and the cycle performance of LIBs. In this study, a sulfate additive, dihydro-1,3,2-dioxathiolo[1,3,2]dioxathiole 2,2,5,5-tetraoxide (DDDT), was used as an efficient multifunctional electrolyte additive for high-voltage lithium cobalt oxide (LiCoO2). Nanoscale protective layers were formed on the surfaces of both the cathode and the anode electrodes by the electrochemical redox reactions, which greatly decreased the side reactions and improved the voltage stability of the electrodes. By adding 2% (wt.%) DDDT into the electrolyte, LiCoO2 exhibited improved Li-storage performance at the relatively high temperature of 60 °C, controlled swelling behavior (less than 10% for 7 days), and excellent cycling performance (capacity retention rate of 76.4% at elevated temperature even after 150 cycles).

Porous graphitic carbon nanorings (PGCNs) are proposed by smart catalytic graphitization of nano-sized graphene quantum dots (GQDs). The as-prepared PGCNs show unique ring-like morphology with diameter around 10 nm, and demonstrate extraordinary mesoporous structure, controllable graphitization degree and highly defective nature. The mechanism from GQDs to PGCNs is proven to be a dissolution-precipitation process, undergoing the procedure of amorphous carbon, intermediate phase, graphitic carbon nanorings and graphitic carbon nanosheets. Further, the relationship between particles size of GQDs precursor and graphitization degree of PGCNs products is revealed. The unique microstructure implies PGCNs a broad prospect for energy storage application. When applied as negative electrode materials in dual-carbon lithium-ion capacitors, high energy density (77.6 Wh·kg −1 ) and super long lifespan (89.5% retention after 40,000 cycles at 5.0 A·g −1 ) are obtained. The energy density still maintains at 24.5 Wh·kg −1 even at the power density of 14.1 kW·kg −1 , demonstrating excellent rate capability. The distinct microstructure of PGCNs together with the strategy for catalytic conversion from nanocarbon precursors to carbon nanorings opens a new window for carbon materials in electrochemical energy storage.

Silicon-carbon composites, which exhibit the advantages of both carbon and silicon materials, are regarded as the most promising anode for lithium ion battery. In this work, a composite of 3D graphene-like nanosheets/silicon wrapped by catalytic graphite (G-3DGNs-Si) was prepared via a chemical oxidation-thermal expansion strategy and high-temperature sintering method. The obvious interlinked 3D-layered spaces in 3DGNs arranged orderly can uniformly accommodate silicon nanoparticles (SiNPs). 3DGNs can relieve the volume expansion and improve the electrical conductivity of SiNPs. In addition, the catalytic graphite evenly coated on the 3DGNs-Si can further improve electrochemical performance. The G-3DGNs-Si composite anode can achieve 90% reversible capacity retention (957.2 mAli g(-1)) at 0.2 A g(-1) after 100 cycles (78.9% after 300 cycles). The method is effective and easy to operate. This work provides a novel idea for designing silicon-carbon composites.

2D carbon materials show extraordinarily promising prospects in energy storage systems. To improve the performance of lithium-ion capacitors (LICs), it is urgently necessary for addressing the sluggish kinetics behavior of battery-type carbon negative electrode. Herein, novel 2D defective high-graphitic carbon nanosheets (GNS), which is derived from in-situ catalytic graphitization of 1D nanorods precursor, are presented and employed as negative electrode materials in LICs. The effects of defects contained in the as-prepared samples are further explored by the First-principle calculations, revealing that carbonylation and N-doping (particularly pyridine N) manifest synergistic effect on improving the electronic conductivity and regulating the microstructure. The high reversible capacity accompanied with large plateau capacity and superior rate capability in the half-cell test implies that GNS can be a promised candidate as negative electrode for LICs. Excitingly, the fabricated LICs exhibit high energy density of 112 Wh kg(-1) and excellent power density of 19,600 W kg(-1), together with outstanding energy density retention of 96.5% after 5000 cycles at 5 A g(-1). The defects-controlled in-situ catalytic strategy for preparing GNS may provide a brand-new way for materials design for energy storage.

Samples of LiMn1-xNixPO4/C (with x = 0, 0.01, 0.03, 0.05 and 0.1) were synthesized using a combination of spray-drying followed by a traditional ball milling method. XRD analysis shows that the Ni doping does not change the structure of the single LiMnPO4 phase, while SEM studies demonstrated that Ni doping can significantly inhibit aggregation of the synthesized compounds. Electrochemical testing indicates that the Ni doped powders have superior performance relative to the un-doped versions. LiMn0.95Ni0.05PO4/C has the best electrochemical performance in the measurements of initial capacity and cycling performance. The first specific discharge capacity of this material is 127.4 mAh.g(-1) at a rate of 0.1 C at 25 degrees C, and it retains 88.9 % of its initial capacity after 50 cycles. Improvement of the electrochemical performance of LiMnPO4/C with Ni doping could be due to improvements in both electrical conductivity and lithium ion diffusion.

Herein, we report a series of O3-type Na(Ni1/3Mn1/3Fe1/3)1-xAlxO2 (x = 0, 0.03, 0.05, 0.07) oxides as sodium-ion battery cathode materials synthesized via spray pyrolysis method. The structure, morphology, and electrochemical performance of Na(Ni1/3Mn1/3Fe1/3)1-xAlxO2 (x = 0, 0.03, 0.05, 0.07) are characterized by XRD, SEM, CV, and galvanostatic charge and discharge tests, respectively. Na(Ni1/3Mn1/3Fe1/3)0.95Al0.05O2 delivers an initial discharge capacity of 145.4 mAh g−1 at 0.1 C and exhibits a favorable reversible capacity about 128.4 mAh g−1 after 80 cycles at 0.2 C, with the capacity retention of 77.5% at the voltage range of 2.0 to 4.2 V. XPS analysis reveals that Al-doping could alleviate the Jahn-Teller effect caused by Mn3+ and enhance the structural stability of layered oxides. The results confirm that a small quantity of (5 at. %) Al-doping improves the structural stability of the material, therefore leading to the excellent electrochemical performance.

A two stage hydrochloric acid leaching process is proposed for the treatment of lepidolite and recovery of alkali metals. The separation characteristics of aluminum and fluoride in the leachate were also determined. The transformation of lepidolite into silica-like residue was tentatively identified through X-ray diffraction measurements. The leach liquor was heated and concentrated and by evaporation to drive off to remove some of the hydrogen chloride and hydrogen fluoride from the acidic leachate, followed by cooling to deposit crystals. This yielded an overall hydrogen chloride and hydrogen fluoride removal of 25.4% and 2.52%, respectively. The main components of the crystals were aluminum and potassium chlorides, with small amounts of fluoroaluminate, polyaluminum chloride, and aluminum hydroxyfluoride. The crystals were calcined at 623 K, with a further 43.9% of hydrogen chloride and 4.33% of hydrogen fluoride being driven off and captured by adsorption equipment, which was beneficial for the subsequent separation of impurities. Investigation of the major mineral phases revealed that lower temperature calcination of the crystals tended to produce less-soluble polyaluminum chloride, aluminum hydroxyfluoride, fluoaluminate, and alumina. Water leaching of crystals after calcination at 623 K gave a leach liquor with 7.74 g/L of lithium, 0.15 g/L of aluminum and 0.25 g/L of fluoride. The fluoaluminate in the leach liquor led to the production of secondary precipitates after neutralization. The [AlFn](3-n) species were partially dissociated to F- and Al(OH)(4)(-) at a strongly basic pH. The residual aluminum and fluoride concentrations were 0.01 g/L and 0.05 g/L, respectively, at the pH of 9. Since alkali chlorides such as lithium chloride are very soluble, there was less lithium loss during neutralization than in the corresponding sulfate system.

Herein, we report a series of O3-type Na(Ni 1/3 Mn 1/3 Fe 1/3 ) 1-x Al x O 2 ( x = 0, 0.03, 0.05, 0.07) oxides as sodium-ion battery cathode materials synthesized via spray pyrolysis method. The structure, morphology, and electrochemical performance of Na(Ni 1/3 Mn 1/3 Fe 1/3 ) 1-x Al x O 2 ( x = 0, 0.03, 0.05, 0.07) are characterized by XRD, SEM, CV, and galvanostatic charge and discharge tests, respectively. Na(Ni 1/3 Mn 1/3 Fe 1/3 ) 0.95 Al 0.05 O 2 delivers an initial discharge capacity of 145.4 mAh g −1 at 0.1 C and exhibits a favorable reversible capacity about 128.4 mAh g −1 after 80 cycles at 0.2 C, with the capacity retention of 77.5% at the voltage range of 2.0 to 4.2 V. XPS analysis reveals that Al-doping could alleviate the Jahn-Teller effect caused by Mn 3+ and enhance the structural stability of layered oxides. The results confirm that a small quantity of (5 at. %) Al-doping improves the structural stability of the material, therefore leading to the excellent electrochemical performance.

Electrochemical performance of a potential fast-charging graphite material in lithium-ion batteries prepared by the modification of natural flake graphite (FG-1) is investigated. FG-1 displays excellent electrochemical performance than most of the modified NFG materials. Galvanostatic cycling tests performed in half cells give the initial capacity of 382.7/361.1 mAh g(-1), delivering a small irreversible capacity (21.6 mAh g(-1)) and high coulombic efficiency (94.4%). The carbon-coated graphite displays superior rate performance at 2 C and 3 C currents in pouch cells. FG-1 can cycle at ambient temperature for 500 times under 2 C/1 C and 3 C/1 C regimes with capacity retention of 90.24% and 86.83%, respectively. Moreover, 86.93% and 86.65% of capacity are retained after 800 cycles at 45 degrees C under the same currents. Storage at elevated temperature (60 degrees C) after 21 days leads to only 2.98% of voltage drop, as well as 75.72% and 86.43% of capacity retention and recovery.

Although the peculiarities of electrodeposition in the preparation of metal hydroxides is quite attractive, adequate interpretation of this process still lacks. Here, a novel interpretation of the electrodeposition of nickel cobalt double layered hydroxides (NiCo-LDHs) is proposed. Different from the traditional strategies implemented in the pure nitrate or nitrate-assisted electrolytic baths, the sulfate solution with thiourea (TU) additive is used. Benefited from the chelating and inducing effects of TU, honeycomb-shaped NiCo-LDH nanosheets can be successfully electrodeposited on nickel foam (NF). When performed as free-standing electrodes, these integrated electrodes show a robust capacitive performance. Specifically, NC2512-15/NF (deposition for 15 min) electrode can deliver remarkable electrochemical properties, such as large capacity (1198 F g(-1) at 1 A g(-1)), excellent rate performance (1000 F g(-1) at 100 A g(-1)) and good cycling stability. Additionally, the NC2512-15/NF//activated carbon (AC) hybrid capacitor (HC) can sustain extraordinary cycle life (88.3% retention for 10,000 cycles) and high energy density (29.1 Wh kg(-1)), further demonstrating the qualified capacitive behavior of NC2512-15/NF electrode. This work provides a new insight into the electrodeposition of metal LDHs based on the design of the electrolyte solution. (C) 2020 Elsevier Ltd. All rights reserved.