Lignin-derived hard carbon anode with a robust solid electrolyte interphase for boosted sodium storage performance

Hard carbon is regarded as a promising anode candidate for sodium-ion batteries due to its low cost,relatively low working voltage,and satisfactory specific capacity.However,it still remains a challenge to obtain a high-performance hard carbon anode from cost-effective carbon sources.In addition,the solid electrolyte interphase(SEI)is subjected to continuous rupture during battery cycling,leading to fast capacity decay.Herein,a lignin-based hard carbon with robust SEI is developed to address these issues,effectively killing two birds with one stone.An innovative gas-phase removal-assisted aqueous washing strategy is developed to remove excessive sodium in the precursor to upcycle industrial lignin into high-value hard carbon,which demonstrated an ultrahigh sodium storage capacity of 359 mAh g^(-1).It is found that the residual sodium components from lignin on hard carbon act as active sites that controllably regulate the composition and morphology of SEI and guide homogeneous SEI growth by a near-shore aggregation mechanism to form thin,dense,and organic-rich SEI.Benefiting from these merits,the as-developed SEI shows fast Na+transfer at the interphases and enhanced structural stability,thus preventing SEI rupture and reformation,and ultimately leading to a comprehensive improvement in sodium storage performance.

Trace Amounts of Triple-Functional Additives Enable Reversible Aqueous Zinc-Ion Batteries from a Comprehensive Perspective

Although their cost-effectiveness and intrinsic safety,aqueous zinc-ion batteries suffer from notorious side reactions including hydrogen evolution reaction,Zn corrosion and passivation,and Zn dendrite formation on the anode.Despite numerous strategies to alleviate these side reactions have been demonstrated,they can only provide limited performance improvement from a single aspect.Herein,a triple-functional additive with trace amounts,ammonium hydroxide,was demonstrated to comprehensively protect zinc anodes.The results show that the shift of electrolyte pH from 4.1 to 5.2 lowers the HER potential and encourages the in situ formation of a uniform ZHS-based solid electrolyte interphase on Zn anodes.Moreover,cationic NH^(4+)can preferentially adsorb on the Zn anode surface to shield the“tip effect”and homogenize the electric field.Benefitting from this comprehensive protection,dendrite-free Zn deposition and highly reversible Zn plating/stripping behaviors were realized.Besides,improved electrochemical performances can also be achieved in Zn//MnO_(2)full cells by taking the advantages of this triple-functional additive.This work provides a new strategy for stabilizing Zn anodes from a comprehensive perspective.

Unraveling the morphological evolution mechanism of solid sulfur species in lithium-sulfur batteries with operando light microscopy

Solid-liquid phase conversion between various sulfur species in lithium-sulfur(Li-S)batteries is a fundamental reaction of the sulfur cathode.Disclosing the morphological evolution of solid sulfur species upon cycling is of great significance to achieving high energy densities.However,an in-depth investigation of the internal reaction is still lacking.In this work,the evolution process of solid sulfur species on carbon substrates is systematically studied by using an operando light microscope combined with in situ electrochemical impedance spectra technology.The observation of phenomena such as bulk solid sulfur species can form and dissolve independently of the conductive substrates and the transformation of supercooled liquid sulfur to crystalline sulfur.Based on the phenomena mentioned above,a possible mechanism was proposed in which the dissolution reaction of solid sulfur species is a spatially free reaction that involves isotropic physical dissolution,diffusion of molecules,and finally the electrochemical reaction.Correspondingly,the formation of solid sulfur species tends to be a form of crystallization in a saturated solution rather than electrodeposition,as is commonly believed.Our findings offer new insights into the reaction of sulfur cathodes and provide new opportunities to design advanced sulfur cathodes for Li-S batteries.

The anodic dissolution kinetics of Mg alloys in water based on ab initio molecular dynamics simulations

The corrosion susceptibility of magnesium(Mg)alloys presents a significant challenge for their broad application.Although there have been extensive experimental and theoretical investigations,the corrosion mechanisms of Mg alloys are still unclear,especially the anodic dissolution process.Here,a thorough theoretical investigation based on ab initio molecular dynamics and metadynamics simulations has been conducted to clarify the underlying corrosion mechanism of Mg anode and propose effective strategies for enhancing corrosion resistance.Through comprehensive analyses of interfacial structures and equilibrium potentials for Mg(0001)/H_(2)O interface models with different water thicknesses,the Mg(0001)/72 H_(2)O model is identified to be reasonable with−2.17 V vs.standard hydrogen electrode equi-librium potential.In addition,utilizing metadynamics,the free energy barrier for Mg dissolution is calculated to be 0.835 eV,enabling the theoretical determination of anodic polarization curves for pure Mg that aligns well with experimental data.Based on the Mg(0001)/72 H_(2)O model,we further explore the effects of various alloying elements on anodic corrosion resistance,among which Al and Mn alloying elements are found to enhance corrosion resistance of Mg.This study provides valuable atomic-scale insights into the corrosion mechanism of magnesium alloys,offering theoretical guidance for developing novel corrosion-resistant Mg alloys.

可逆阴离子氧化还原反应和结构演变的共生P2/O3双相钠离子电池层状氧化物正极设计和开发

层状氧化物因在钠离子电池正极中表现出的优异性能而引起了前所未有的关注,其中两种典型的P2和03型材料各具优势.因此,设计和开发包含P2和03材料的复合材料成为一种新的选择.但对这种具有多相结构的复杂正极材料的阴离子/阳离子的行为和结构演变过程的研究仍缺乏全面且深入的研究.本文基于两种典型的具有相同元素组成但不同的晶体结构的正极材料:P2型Na0.67Ni0.33Mn0.67O2和O3型NaNi0.5Mn0.5O2,开发了一种成分为Na0.732Ni0.273Mg0.096Mn0.63O2的双相材料,其中包含78.39 wt%的P2相和21.61 wt%的O3相.晶体结构分析和密度泛函理论(DFT)计算结果表明,该复合材料倾向于形成原子水平上的共生结构,且形成的双相结构的复杂晶格条纹可以阻止电极过程中过渡金属和氧原子迁移.相对于单相结构,双相结构提高了正极材料的储钠容量和稳定性,并增强了阴离子O2-/n-氧化还原的可逆性.此外,P2和O3结构共生的类异质结结构具有共享相边界,其形成的互锁效应可有效缓解P2和03结构在电极过程产生的晶格滑移和Na+离子脱出/嵌入的晶格应力.因此,共生的P2/03复合材料表现出较高的容量、较好的循环性能(0.1 C倍率下约有130 mAh g-1容量,循环200次后容量保持率为73.1%)和可逆的晶体结构转变.本文研究证实合理设计的双/多相正极可用于高能钠离子电池的应用.

Understanding and tuning negative longitudinal piezoelectricity in hafnia

Most piezoelectric materials exhibit a positive longitudinal piezoelectric effect(PLPE),while a negative longitudinal piezoelectric effect(NLPE)is rarely reported or paid much attention.Here,utilizing firstprinciples calculations,we unveil the origin of negative longitudinal piezoelectricity in ferroelectric hafnia by introducing the concept of weighted projected bond strength around cation in the c direction(WPBc),which is proposed to quantitatively characterize the asymmetric bonding stiffness along the strain direction.When the WPBc is anti-parallel to the direction of bulk spontaneous polarization,the polarization decreases with respect to tensile strain and leads to a negative piezoelectricity.