Chemically Prelithiated Hard-Carbon Anode for High Power and High Capacity Li-Ion Batteries.

Hard carbons (HC) have potential high capacities and power capability, prospectively serving as an alternative anode material for Li-ion batteries (LIB). However, their low initial coulombic efficiency (ICE) and the resulting poor cyclability hinder their practical applications. Herein, a facile and effective approach is developed to prelithiate hard carbons by a spontaneous chemical reaction with lithium naphthalenide (Li-Naph). Due to the mild reactivity and strong lithiation ability of Li-Naph, HC anode can be prelithiated rapidly in a few minutes and controllably to a desirable level by tuning the reaction time. The as-formed prelithiated hard carbon (pHC) has a thinner, denser, and more robust solid electrolyte interface layer consisting of uniformly distributed LiF, thus demonstrating a very high ICE, high power, and stable cyclability. When paired with the current commercial LiCoO2 and LiFePO4 cathodes, the assembled pHC/LiCoO2 and pHC/LiFePO4 full cells exhibit a high ICE of >95.0% and a nearly 100% utilization of electrode-active materials, confirming a practical application of pHC for a new generation of high capacity and high power LIBs.

Surface Modification of Fe7 S8 /C Anode via Ultrathin Amorphous TiO2 Layer for Enhanced Sodium Storage Performance.

Iron sulfides with high theoretical capacity and low cost have attracted extensive attention as anode materials for sodium ion batteries. However, the inferior electrical conductivity and devastating volume change and interface instability have largely hindered their practical electrochemical properties. Here, ultrathin amorphous TiO2 layer is constructed on the surface of a metal-organic framework derived porous Fe7 S8 /C electrode via a facile atomic layer deposition strategy. By virtue of the porous structure and enhanced conductivity of the Fe7 S8 /C, the electroactive TiO2 layer is expected to effectively improve the electrode interface stability and structure integrity of the electrode. As a result, the TiO2 -modified Fe7 S8 /C anode exhibits significant performance improvement for sodium-ion batteries. The optimal TiO2 -modified Fe7 S8 /C electrode delivers reversible capacity of 423.3 mA h g-1 after 200 cycles with high capacity retention of 75.3% at 0.2 C. Meanwhile, the TiO2 coating is conducive to construct favorable solid electrolyte interphase, leading to much enhanced initial Coulombic efficiency from 66.9% to 72.3%. The remarkable improvement suggests that the interphase modification holds great promise for high-performance metal sulfide-based anode materials for sodium-ion batteries.

Highly Electrochemically-Reversible Mesoporous Na2 FePO4 F/C as Cathode Material for High-Performance Sodium-Ion Batteries.

As promising cathode materials, iron-based phosphate compounds have attracted wide attention for sodium-ion batteries due to their low cost and safety. Among them, sodium iron fluorophosphate (Na2 FePO4 F) is widely noted due to its layered structure and high operating voltage compared with NaFePO4 . Here, a mesoporous Na2 FePO4 F@C (M-NFPF@C) composite derived from mesoporous FePO4 is synthesized through a facile ball-milling combined calcination method. Benefiting from the mesoporous structure and highly conductive carbon, the M-NFPF@C material exhibits a high reversible capacity of 114 mAh g-1 at 0.1 C, excellent rate capability (42 mAh g-1 at 10 C), and good cycling performance (55% retention after 600 cycles at 5 C). The high plateau capacity obtained (>90% of total capacity) not only shows high electrochemical reversibility of the as-prepared M-NFPF@C but also provides high energy density, which mainly originates from its mesoporous structure derived from the mesoporous FePO4 precursor. The M-NFPF@C serves as a promising cathode material with high performance and low cost for sodium-ion batteries.

What can we learn from the Baduanjin rehabilitation as COVID-19 treatment?: A narrative review.

AIM: To understand Baduanjin rehabilitation therapy in mild COVID-19 patients. DESIGN: A narrative review. METHODS: A literature search for COVID-19 and Baduanjin treatments was conducted on Chinese and English electronic databases: China National Knowledge Infrastructure, Wanfang Data, Embase, PubMed, Scopus, Science Direct, Ebscohost, SPORTDiscus and ProQuest. RESULTS: Twelve studies on the Baduanjin rehabilitation for COVID-19 patients have been included. We acknowledged the considerable published research and current clinical practice using Baduanjin for COVID-19 treatment in the following areas: anxiety, depression, insomnia, lung function rehabilitation, immunity and activity endurance. CONCLUSION: The use of Baduanjin as adjuvant therapy for COVID-19 patients' rehabilitation is still limited, therefore, more clinical studies are needed to confirm its efficacy.

Revealing the structural chemistry in Na6-2xFex(SO4)3 (1.5 ≤ x ≤ 2.0) for low-cost and high-performance sodium-ion batteries.

Fe-based polyanionic sulfate materials are one of the most promising candidates for large-scale applications in sodium-ion batteries due to their low cost and excellent electrochemical performance. Although great achievements have been gained on a series of Na6-2xFex(SO4)3 (NFSO-x, 1.5 ≤ x ≤ 2.0) materials such as Na2Fe2(SO4)3, Na2Fe1.5(SO4)3, and Na2.4Fe1.8(SO4)3 for sodium storage, the phase and structure characteristics on these NFSO-x are still controversial, making it difficult to achieve phase-pure materials with optimal electrochemical properties. Herein, six NFSO-x samples with varied x are investigated via both experimental methods and density functional theory calculations to analyze the phase and structure properties. It reveals that a pure phase exists in the 1.6 ≤ x ≤ 1.7 region of the NFSO-x, and part of Na ions tend to occupy Fe sites to form more stable frameworks. The NFSO-1.7 exhibits the best electrochemical performance among the NFSO-x samples, delivering a high discharge capacity (104.5 mAh g-1 at 0.1 C, close to its theoretical capacity of 105 mAh g-1), excellent rate performance (81.5 mAh g-1 at 30 C), and remarkable cycle stability over 10,000 cycles with high-capacity retention of 72.4%. We believe that the results are useful to clarify the phase and structure characteristics of polyanionic materials to promote their application for large-scale energy storage.

All-Climate High-Voltage Commercial Lithium-Ion Batteries Based on Propylene Carbonate Electrolytes.

Propylene carbonate (PC)-based electrolytes have many attractive advantages over the commercially used ethylene carbonate (EC)-based electrolytes like a wider operating temperature and higher oxidation stability. Therefore, PC-based electrolytes become the potential candidate for lithium-ion batteries with higher energy density, longer lifespan, and better low- and high-temperature performance. In spite of the superiority, PC is incompatible with the graphite anode because PC fails to passivate the graphite anode, leading to severe decomposition and gas evolution, which seriously restrict the development of the PC-based electrolytes. Nevertheless, it is recently found that the usage of diethyl carbonate (DEC) as a cosolvent will greatly improve the anodic tolerance of PC to realize the reversible lithiation/delithiation of the graphite anode in the PC-based electrolyte. It is because DEC induces anions into the solvation shell of Li+ to form an anion-induced ion-solvent-coordinated (AI-ISC) structure with higher reduction stability. In this work, we fabricated 4.4 V pouch cells to assess in detail the practical viability of the PC-based electrolyte in a commercial battery system. In comparison to conventionally used EC-based cells, the pouch cells with the PC-based electrolyte exhibit more excellent high-voltage tolerance and electrochemical performance at all temperature ranges (-40 to 85 °C), demonstrating the wide application prospect of the PC-based electrolyte.

High-Voltage and Intrinsically Safe Sodium Metal Batteries Enabled by Nonflammable Fluorinated Phosphate Electrolytes.

Sodium metal is a promising anode for high-energy-density sodium rechargeable batteries (RSBs). However, the low Coulombic efficiency (CE) of the Na plating/stripping process and the problem of safety hinder their practical application. Herein, we report a facile strategy for employing the fluorinated phosphate solvents to realize highly reversible Na plating/stripping and improve the safety performance. The fluorinated phosphate molecules reduce the polarity of the solvent and lower the coordination number to Na+, which makes it possible to form the anion-induced ion-solvent-coordinated (AI-ISC) structures with high reduction tolerance. Moreover, the fluorination treatment enhances the oxidation resistance of the phosphate solvent, enabling compatibility with the high-voltage Na3V2(PO4)2F3 (NVPF) cathode. As expected, the Na@Al//NVPF full cell with the as-prepared 0.9 M NaFSI/tris(2,2,2-trifluoroethyl) phosphate (TFEP) demonstrates a capacity retention of 83.4% after 200 cycles with an average CE of 99.6%. This work opens a new avenue for designing high-energy-density RSBs with improved safety performance.

Efficient and Facile Electrochemical Process for the Production of High-Quality Lithium Hexafluorophosphate Electrolyte.

The global consumption for lithium hexafluorophosphate (LiPF6) has increased dramatically with the rapid growth of Li-ion batteries (LIBs) for large-scale electric energy storage applications. Conventional LiPF6 production has a high cost and high energy consumption due to complicated separation and purification processes. Here, based on the electrode materials of LiMn2O4 and polyaniline (PANI), we propose a facile electrochemical extraction/release process for LiPF6 electrolyte production. This new technology consists of two independent steps: a PF6-- and Li+-extracting step using a PANI/LixMn2O4 cell in aqueous solution (an ion extraction step) and a LiPF6 electrolyte production step from the charged LiMn2O4/PANI+PF6- cell in an organic electrolyte (an ion release step). This new process can effectively avoid the contamination of HF residue in the final product, providing a great possibility to create a facile, energy-efficient, and low-cost LiPF6 electrolyte production.

Building a Cycle-Stable Fe-Si Alloy/Carbon Nanocomposite Anode for Li-Ion Batteries through a Covalent-Bonding Method.

Si is being intensively developed as a safe and high-performance anode for next-generation Li-ion batteries (LIBs); however, its battery application still remains challenging because of its low cycling Coulombic efficiency. To address this issue, we chose a conjugated polymer, polynaphthalene, as a carbon precursor and a low-cost commercial ferrosilicon (Fe-Si) alloy as the active phase to prepare a Fe-Si/C nanocomposite with a core-shell-like architecture through sand milling-assisted covalent-bonding method, followed by a carbonization reaction, thus forming a covalently bonded carbon coating on the surfaces of Fe-Si alloy nanoparticles. Benefitting from the greatly reduced volumetric expansion of Fe-Si alloy cores in the lithiation process and the stable interface provided by the outer carbon shell, the thus-prepared Fe-Si/C nanocomposite exhibits a high structural stability in repeated charge/discharge cycles. The experimental results reveal that the Fe-Si/C composite anode can demonstrate a high reversible capacity of 1316.2 mA h g-1 with an active mass utilization of 82.6%, a long-term cycle stability of more than 1000 cycles even at a considerably high current rate of 2.0 A g-1, and, in particular, a high cycling Coulombic efficiency of 99.7%, showing great prospect for application in practical LIBs.

Covalently Bonded Silicon/Carbon Nanocomposites as Cycle-Stable Anodes for Li-Ion Batteries.

Carbon coating is a popular strategy to boost the cyclability of Si anodes for Li-ion batteries. However, most of the Si/C nanocomposite anodes fail to achieve stable cycling due to the easy separation and peeling off of the carbon layer from the Si surface during extended cycles. To overcome this problem, we develop a covalent modification strategy by chemically bonding a large conjugated polymer, poly-peri-naphthalene (PPN), on the surfaces of nano-Si particles through a mechanochemical method, followed by a carbonization reaction to convert the PPN polymer into carbon, thus forming a Si/C composite with a carbon coating layer tightly bonded on the Si surface. Due to the strong covalent bonding interaction of the Si surface with the PPN-derived carbon coating layer, the Si/C composite can keep its structural integrity and provide an effective surface protection during the fluctuating volume changes of the nano-Si cores. As a consequence, the thus-prepared Si/C composite anode demonstrates a reversible capacity of 1512.6 mA h g-1, a stable cyclability over 500 cycles with a capacity retention of 74.2%, and a high cycling Coulombic efficiency of 99.5%, providing a novel insight for designing highly cyclable silicon anodes for new-generation Li-ion batteries.

Enabling electrochemical compatibility of non-flammable phosphate electrolytes for lithium-ion batteries by tuning their molar ratios of salt to solvent.

We develop a new type of electrolyte with a high molar ratio (MR) of salt to solvent but a low molar concentration by adjusting the molar mass of the solvent. The present 1 : 2 LiFSI-triamyl phosphate electrolyte exhibits a low molar concentration of only 1.35 M along with excellent electrochemical stability against the graphite anode.

A Membrane-Free and Energy-Efficient Three-Step Chlor-Alkali Electrolysis with Higher-Purity NaOH Production.

Conventional chlor-alkali processes are energy-consuming and environmentally unfriendly. To deal with this problem, we developed a three-step electrolysis (TSE) for a cleaner, energy-saving, and lower-cost chlor-alkali process. This new chlor-alkali process consists of three independent steps: a NaOH-production step in a Na0.44MnO2/oxygen-depolarizing cathode cell (step I), a Na+ and CI- extraction step in a Ag/Na0.44-xMnO2 cell (step II), and a CI2-production step in a graphite/AgCl cell (step III). This technology avoids the use of expensive ion-exchange membrane and toxic electrode materials, providing a great prospect to create a cleaner, energy-saving, and lower-cost chlor-alkali electrolysis process. This electrochemical ion coupling/decoupling technology can also be extended to other salt solutions (Na2SO4/NaNO3) to produce corresponding alkali (NaOH) and acid (H2SO4/HNO3), which has potential significance in the chlor-alkali industry.

Hollow carbon nanofibers as high-performance anode materials for sodium-ion batteries.

Hollow carbon nanofibers (HCNFs) are successfully fabricated by pyrolyzation of a polyaniline hollow nanofiber precursor. The as-prepared HCNFs as sodium storage anode materials exhibit a high reversible charge capacity of 326 mA h g-1 at 20 mA g-1, high rate capability (85 mA h g-1 at 1.6 A g-1) and superior cycling stability (a capacity retention of 70% even after 5000 cycles at 1.6 A g-1). Such a high performance of HCNFs can be ascribed to the special hollow structure characteristics; they possess a well fabricated electronic transport path and can shorten the ion diffusion distance. Therefore, the HCNFs can be regarded as promising anode materials for advanced sodium ion batteries (SIBs).

High-Safety Symmetric Sodium-Ion Batteries Based on Nonflammable Phosphate Electrolyte and Double Na3V2(PO4)3 Electrodes.

Sodium-ion batteries (SIBs) have been viewed as a promising candidate for grid-scale energy storage systems owing to their low cost and abundant Na resources. However, insufficient safety and poor cycling performance of current SIBs are hampering their implementation. Herein, we develop a symmetric SIB by employing Na3V2(PO4)3 as both cathode and anode along with the nonflammable triethyl phosphate dissolving 0.9 M NaClO4 as the electrolyte. The symmetric SIB demonstrates a superior rate capability (35.1 mA h g-1 at 32 C) and excellent cycling performance with a capacity retention of 88.9% after 500 cycles at 2 C. This work demonstrates a new avenue to construct safe and long-cycle-life SIBs with a simple electrode manufacturing process.

Understanding the Electrochemical Compatibility and Reaction Mechanism on Na Metal and Hard Carbon Anodes of PC-Based Electrolytes for Sodium-Ion Batteries.

Electrolytes as an important part of sodium-ion batteries have a pivotal role for capacity, rate, and durability of electrode materials. On account of the high reduction activity of sodium metal with organic solvents, it is very important to optimize the electrolyte component to realize high stability on Na metal and hard carbon anodes. Herein, chemical and electrochemical stability of propylene carbonate (PC)-based electrolytes on sodium metal and hard carbon anodes is investigated systematically. The results demonstrate that whether using NaClO4 or NaPF6, the PC-based electrolytes are not stable on Na metal, but adding of FEC can immensely enhance the stability of the electrolyte because of the compact solid electrolyte interphase film formed. The electrolytes containing FEC also exhibit high electrochemical compatibility on hard carbon anodes, showing high reversible capacity and excellent cycling performance. A reaction mechanism based on the Na+ induction effect is proposed by spectrum and electrochemical measurements. This study can provide a new insight to optimize and develop stable PC-based electrolytes and be helpful for understanding the other electrolyte systems.

High Capacity and Cycle-Stable Hard Carbon Anode for Nonflammable Sodium-Ion Batteries.

Nonflammable phosphate electrolytes are in principle able to build intrinsically safe Na-ion batteries, but their electrochemical incompatibility with anodic materials, especially hard carbon anode, restricts their battery applications. Here, we propose a new strategy to enable high-capacity utilization and cycle stability of hard carbon anodes in the nonflammable phosphate electrolyte by using low-cost Na+ salt with a high molar ratio of salt/solvent combined with an solid electrolyte interphase film-forming additive. As a result, the carbon anode in the trimethyl phosphate (TMP) electrolyte with a high molar ratio of [NaClO4]/[TMP] and 5% fluoroethylene carbonate additive demonstrates a high reversible capacity of 238 mAh g-1, considerable rate capability, and long-term cycling life with 84% capacity retention over 1500 cycles. More significantly, this work provides a promising route to build intrinsically safe and low-cost sodium-ion batteries for large-scale energy storage applications.