A Universal Molten Salt Method for Direct Upcycling of Spent Ni-rich Cathode towards Single-crystalline Li-rich Cathode.

With ever-increasing pursuit for high-value output in recycling spent lithium-ion batteries (LIBs), traditional recycling methods of cathodes tend to be obsolete because of the complicated procedures. Herein, we first upcycle spent polycrystal LiNi0.88 Co0.095 Al0.025 O2 (S-NCA) to high value-added single-crystalline and Li-rich cathode materials through a simple but feasible LiOH-Na2 SO4 eutectic molten salt strategy. The in situ X-ray diffraction technique and a series of paratactic experiments record the evolution process of upcycling and prove that excessive Li occupies the transition metal (TM) layers. Beneficial from the single-crystalline and Li-rich nature, the regenerated NCA (R-NCA) exhibits remarkably enhanced electrochemical performances in terms of long-term cyclability, high-rate performance and low polarization. This approach can also be successfully extended to other cathode materials e.g., LiNix Coy Mnz O2 (NCM) and mixed spent NCAs with varied degree of Li loss.

A Ternary Molten Salt Approach for Direct Regeneration of LiNi0.5 Co0.2 Mn0.3 O2 Cathode.

Recycling spent lithium-ion batteries (LIBs) is an urgent task in view of the resource shortage and environmental concerns. Here, a facile ternary molten salt approach is presented for efficiently regenerating the LiNi0.5 Co0.2 Mn0.3 O2 (NCM523) cathode of spent LIBs. Such an approach involves the treatment of spent cathode powder in the ternary molten salt at a moderate temperature (400 °C) and subsequent annealing in oxygen. The Li loss and degraded phases in spent NCM that cause the capacity decay can be fully remedied after the regeneration process. As a result, the regenerated cathode delivers a reversible capacity of 160 mAh g-1 at 0.5 C with retention of 93.7% after 100 cycles and maintains a high capacity of 132 mAh g-1 at a high rate of 5 C. The electrochemical performance of regenerated NCM cathode is compared favorably to the fresh NCM cathode, which demonstrates the feasibility of the molten salt approach to directly regenerate spent NCM cathode.

Self-Reconstruction of Highly Degraded LiNi0.8 Co0.1 Mn0.1 O2 toward Stable Single-Crystalline Cathode.

The ever-growing demand for resources sustainability has promoted the recycle of spent lithium-ion batteries to a strategic position. Direct recycle outperforms either hydrometallurgical or pyrometallurgical approaches due to the high added value and facile treatment processes. However, the traditional direct recycling technologies are only applicable for Ni-poor/middle cathodes. Herein, spent Ni-rich LiNi0.8 Co0.1 Mn0.1 O2 (S-NCM) to performance-enhanced single-crystalline cathode materials is directly recycled using a simple but effective LiOH-NaCl molten salt. The evolution process of the Li-supplement and grain-recrystallization during regeneration is systematically investigated, and the successful recovery of the highly degraded microstructure is comprehensively proven, including significant elimination of Ni2+ and O vacancies. Beneficial from the favorable reconstructed single-crystalline particles, the regenerated NCM (R-NCM) represents remarkably enhanced structural stability, electrochemical activity, O2 and cracks suppression during charge/discharge, thus achieving the excellent performances in long-term cycling and high-rate tests. As a result, R-NCM maintains the 86.5% reversible capacity at 1 C after 200 cycles. Instructively, the present molten salt can be successfully applied for recycling spent NCMs with various Li and Ni compositions (e.g., LiNi0.5 Co0.2 Mn0.3 O2 ).

Electrochemical reconfiguration of iron-modified Ni3S2 surface induced oxygen vacancies to immobilize sulfate for enhanced oxygen evolution reaction.

There is an urgent need for highly active, durable, and low-cost electrocatalysts to overcome the shortcomings of high overpotential in the oxygen evolution reaction (OER) process. In this work, the nickel-iron hydroxysulfate rich in sulfate and oxygen vacancies (SO42-@Fe-NiOOH-Ov/NiS) is legitimately constructed. SO42-@Fe-NiOOH-Ov/NiS only requires a low overpotentials of 190 mV and 232 mV at 10 mA cm-2 and 100 mA cm-2 current densities in 1 M KOH, with excellent stability for 200 h at 100 mA cm-2 current density. In situ Raman spectroscopy and Fourier transform infrared spectroscopy demonstrated the stable adsorption of more SO42- on the surface of catalyst. Density functional theory calculations testify surface reconstruction, doped Fe and oxygen vacancies significantly reduced the adsorption energy of sulfate on the surface. More importantly, the formation of *OOH to O2 is facilitated by the highly hydrogen bonding between SO42- and *OOH, accelerating the OER process.

Structural equation model was used to evaluate the effects of soil chemical environment, fertility and enzyme activity on eucalyptus biomass.

This paper aims to reveal the effects of multi-generational succession of eucalyptus on soil fertility, organic structure and biological properties. Soil samples were collected from eucalyptus plantations of different stand ages (5, 11, 17 and 21 years old) in a typical area in south Asia, soil organic fraction structure and content characteristics were investigated using Fourier transform infrared (FTIR), and structural equation modelling (SEM) was used to explore influences of soil fertility, enzyme activity and organic fraction on stand biomass. FTIR analysis showed that 11 infrared absorption peaks existed in the soils of this study area, attributed to silicates, aromatics, carbonate ions, sugars, esters, polysaccharides, aliphatic hydrocarbons and phenolic alcohols. Combined with the results of peak area integration, the content of esters, aromatics and phenolic alcohols was significantly higher in 17- and 21-year-old stand soils than in control soils. The results of SEM showed that organic components were negatively related (p < 0.01) to enzyme activity and biomass, with standardized coefficients of 0.53 and 0.49, respectively. In summary, multi-generation succession of eucalyptus trees can change the structure of soil organic functional group composition and promote the enrichment of aromatic and phenolic alcohol functional groups. Such changes can directly inhibit the increase in eucalyptus biomass and indirectly negatively affect biomass by inhibiting enzyme activity.

Electrochemical surface reconstruction of Prussian blue-modified nickel sulfide to form iron-nickel bilayer hydroxyl oxides for efficient and stable oxygen evolution reaction processes.

The oxygen evolution reaction (OER) is an important semi-reaction in the electrocatalytic water splitting for hydrogen energy production, and the development of efficient and low-cost electrocatalysts to solve the problem of slow 4-electron transport kinetics in the OER process is key. In this work, a pre-electrocatalyst with the heterogeneous interfacial structure, Prussian blue-modified nickel sulfide with sulfur vacancies (PB/NS-Sv), was designed and then converted to iron-nickel bilayer hydroxyl oxides in oxygen-rich vacancies (FeOOH/NiOOH-Ov@NS) through electrochemical oxidative reconstruction to obtain a truly stable and efficient active material. The study utilized in situ Raman to observe the transition from PB/NS-Sv to FeOOH/NiOOH-Ov@NS during the reaction. The electronic density of states in FeOOH/NiOOH-Ov@NS is regulated by the bilayer hydroxyl metal oxide synergistic effect and the abundant oxygen defect of Mental-OOH-Ov, which significantly improves OER catalytic performance. FeOOH/NiOOH-Ov@NS requires a low overpotential of only 257 mV in 1 mol/L KOH at 100 mA cm-2 current density, has a small Tafel slope of 35.2 mV dec-1 and has excellent stability for 150 h at 100 mA cm-2 current density, making it a promising candidate for industrial applications.

Hyperspectral band selection and modeling of soil organic matter content in a forest using the Ranger algorithm.

Effective soil spectral band selection and modeling methods can improve modeling accuracy. To establish a hyperspectral prediction model of soil organic matter (SOM) content, this study investigated a forested Eucalyptus plantation in Huangmian Forest Farm, Guangxi, China. The Ranger and Lasso algorithms were used to screen spectral bands. Subsequently, models were established using four algorithms: partial least squares regression, random forest (RF), a support vector machine, and an artificial neural network (ANN). The optimal model was then selected. The results showed that the modeling accuracy was higher when band selection was based on the Ranger algorithm than when it was based on the Lasso algorithm. ANN modeling had the best goodness of fit, and the model established by RF had the most stable modeling results. Based on the above results, a new method is proposed in this study for band selection in the early phase of soil hyperspectral modeling. The Ranger algorithm can be applied to screen the spectral bands, and ANN or RF can then be selected to construct the prediction model based on different datasets, which is applicable to establish the prediction model of SOM content in red soil plantations. This study provides a reference for the remote sensing of soil fertility in forests of different soil types and a theoretical basis for developing portable equipment for the hyperspectral measurement of SOM content in forest habitats.