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1. WS2 Nanosheet Loaded Silicon-Oxycarbide Electrode for Sodium and Potassium Batteries

   https://doi.org/10.3390/nano12234185  

   Dey, Sonjoy; Singh, Gurpreet (December 2022, Nanomaterials)

   Transition metal dichalcogenides (TMDs) such as the WS2 have been widely studied as potential electrode materials for lithium-ion batteries (LIB) owing to TMDs’ layered morphology and reversible conversion reaction with the alkali metals between 0 to 2 V (v/s Li/Li+) potentials. However, works involving TMD materials as electrodes for sodium- (NIBs) and potassium-ion batteries (KIBs) are relatively few, mainly due to poor electrode performance arising from significant volume changes and pulverization by the larger size alkali-metal ions. Here, we show that Na+ and K+ cyclability in WS2 TMD is improved by introducing WS2 nanosheets in a chemically and mechanically robust matrix comprising precursor-derived ceramic (PDC) silicon oxycarbide (SiOC) material. The WS2/SiOC composite in fibermat morphology was achieved via electrospinning followed by thermolysis of a polymer solution consisting of a polysiloxane (precursor to SiOC) dispersed with exfoliated WS2 nanosheets. The composite electrode was successfully tested in Na-ion and K-ion half-cells as a working electrode, which rendered the first cycle charge capacity of 474.88 mAh g−1 and 218.91 mAh g−1, respectively. The synergistic effect of the composite electrode leads to higher capacity and improved coulombic efficiency compared to the neat WS2 and neat SiOC materials in these cells. 

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2. Impacts of fluorine in NASICON‐type materials as cathodes for aqueous zinc ion batteries

   https://doi.org/10.1002/ese3.925  

   Liu, Ziyan; Jia, Xiaoxiao; Cao, Guozhong (May 2021, Energy Science & Engineering)

   Abstract Sodium superionic conductor (NASICON)‐type materials are getting more and more attention due to their high capacity and good cycling ability compared with other cathode materials in aqueous zinc ion batteries (AZIB). The present paper was to study the synthesis and electrochemical properties of two NASICON compounds of Na₃V₂(PO₄)₃and Na₃V₂(PO₄)₂F₃and to understand the impacts of fluorine. Both Na₃V₂(PO₄)₃and Na₃V₂(PO₄)₂F₃are synthesized by hydrothermal growth followed with annealing at 800°C in inert gas. With 3 mol/L Zn(CF₃SO₃)₂in water as electrolyte, Na₃V₂(PO₄)₃offered a high storage capacity, while Na₃V₂(PO₄)₂F₃demonstrated a high discharge voltage though low storage capacity. It was also found that the storage capacity of Na₃V₂(PO₄)₂F₃increases with increased cycles; however, the compound undergoes a gradual phase transition. It is discussed possible approaches to attain both high discharge voltage and large capacity with good cycling stability. 

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3. NaCa _0.6 V ₆ O ₁₆ ·3H ₂ O as an Ultra‐Stable Cathode for Zn‐Ion Batteries: The Roles of Pre‐Inserted Dual‐Cations and Structural Water in V ₃ O ₈ Layer

   https://doi.org/10.1002/aenm.201901968  

   Zhu, Kaiyue; Wu, Tao; Huang, Kevin (August 2019, Advanced Energy Materials)

   Abstract Rechargeable aqueous batteries with Zn²⁺as a working‐ion are promising candidates for grid‐scale energy storage because of their intrinsic safety, low‐cost, and high energy‐intensity. However, suitable cathode materials with excellent Zn²⁺‐storage cyclability must be found in order for Zinc‐ion batteries (ZIBs) to find practical applications. Herein, NaCa_0.6V₆O₁₆·3H₂O (NaCaVO) barnesite nanobelts are reported as an ultra‐stable ZIB cathode material. The original capacity reaches 347 mAh g⁻¹at 0.1 A g⁻¹, and the capacity retention rate is 94% after 2000 cycles at 2 A g⁻¹and 83% after 10 000 cycles at 5 A g⁻¹, respectively. Through a combined theoretical and experimental approach, it is discovered that the unique V₃O₈layered structure in NaCaVO is energetically favorable for Zn²⁺diffusion and the structural water situated between V₃O₈layers promotes a fast charge‐transfer and bulk migration of Zn²⁺by enlarging gallery spacing and providing more Zn‐ion storage sites. It is also found that Na⁺and Ca²⁺alternately suited in V₃O₈layers are the essential stabilizers for the layered structure, which play a crucial role in retaining long‐term cycling stability. 

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4. In Operando Strain Evolution in Sodium Chromium Oxide Cathode for Na-Ion Batteries during Battery Cycling

   https://doi.org/10.1149/MA2023-015879mtgabs  

   Wable, Minal; Bal, Batuhan; Capraz, Omer_Ozgur Özgür (August 2023, ECS Meeting Abstracts)

   Layer-structured Na intercalation compounds such as NaxMO2 (M=Co, Mn, Cr) have attracted much attention as cathode materials for sodium-ion batteries due to their high volumetric and gravimetric energy densities. Among them, NaCrO2 with layered rock salt structure is one of the promising cathodes since NaCrO2 has a desirable flat and smooth charge/discharge voltage plateau.1 In addition, NaCrO2 has the highest thermal stability at charged state which makes it a potentially safer cathode material.2 The NaCrO2 exhibits a reversible capacity of 110 mAh g-1 with good cycling performance.3 However, the transition metal oxide (TMO) cathode materials in NIBs undergo severe chemo-mechanical deformations which leads to capacity fade and poor cycling and is the limiting factor of NIBs. The electrochemical characterization and examination of the electrode structure were the primary focus of several investigations. To improve the lifespan and performance of electrode materials for Na-ion batteries, it is vital to comprehend how Na ions impact the chemo-mechanical stability of the electrodes. In this talk, we will discuss the driving forces behind the structural and interfacial deformations on NaCrO2 cathodes. Digital image correlation measurements were conducted to probe strain evolution in the electrode during cycling. The free-standing composite NaCrO2 electrode was used for stain measurements in custom-cell assembly. The battery was cycled against Na metal in 1 M NaClO4 in PC. The first part of the study involves structural and interfacial deformations in the lower voltage range of 2.3 V to 3.5 V where x<0.5 in NaxCrO2. And the second part focuses on the structural and interfacial deformations in the voltage range of 2.3 V to 4.7 V where x>0.5 in NaxCrO2. In the preliminary studies, we observed that the initial insertion of Na ions leads to negative strain evolution (contraction) in the electrode, followed by expansions in the electrode at a higher state of discharge. Similar phenomena are also observed during charge cycles, where extraction of Na results in an initial contraction in the electrode, followed by expansion at a higher state of charge. Understanding the mechanisms behind chemo-mechanical deformations will allow to tune structure & material property for better electrochemical performance. 

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5. Concentrated ternary ether electrolyte allows for stable cycling of a lithium metal battery with commercial mass loading high‐nickel NMC and thin anodes

   https://doi.org/10.1002/cey2.275  

   Yang, Jun; Li, Xing; Qu, Ke; Wang, Yixian; Shen, Kangqi; Jiang, Changhuan; Yu, Bo; Luo, Pan; Li, Zhuangzhi; Chen, Mingyang; et al (March 2023, Carbon Energy)

   Abstract A new concentrated ternary salt ether‐based electrolyte enables stable cycling of lithium metal battery (LMB) cells with high‐mass‐loading (13.8 mg cm⁻², 2.5 mAh cm⁻²) NMC622 (LiNi_0.6Co_0.2Mn_0.2O₂) cathodes and 50 μm Li anodes. Termed “CETHER‐3,” this electrolyte is based on LiTFSI, LiDFOB, and LiBF₄with 5 vol% fluorinated ethylene carbonate in 1,2‐dimethoxyethane. Commercial carbonate and state‐of‐the‐art binary salt ether electrolytes were also tested as baselines. With CETHER‐3, the electrochemical performance of the full‐cell battery is among the most favorably reported in terms of high‐voltage cycling stability. For example, LiNi_xMn_yCo_1–x–yO₂(NMC)‐Li metal cells retain 80% capacity at 430 cycles with a 4.4 V cut‐off and 83% capacity at 100 cycles with a 4.5 V cut‐off (charge at C/5, discharge at C/2). According to simulation by density functional theory and molecular dynamics, this favorable performance is an outcome of enhanced coordination between Li⁺and the solvent/salt molecules. Combining advanced microscopy (high‐resolution transmission electron microscopy, scanning electron microscopy) and surface science (X‐ray photoelectron spectroscopy, time‐of‐fight secondary ion mass spectroscopy, Fourier‐transform infrared spectroscopy, Raman spectroscopy), it is demonstrated that a thinner and more stable cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) are formed. The CEI is rich in lithium sulfide (Li₂SO₃), while the SEI is rich in Li₃N and LiF. During cycling, the CEI/SEI suppresses both the deleterious transformation of the cathode R‐3m layered near‐surface structure into disordered rock salt and the growth of lithium metal dendrites. 

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