Confined Red Phosphorus in Edible Fungus Slag-Derived Porous Carbon as an Improved Anode Material in Sodium-Ion Batteries

Red phosphorus (RP) as the anode material for the sodium-ion battery (SIB) possesses a high energy density, but the poor electronic conductivity and huge volume change during Na⁺ insertion/extraction restrict its application. In this work, the edible fungus slag-derived porous carbon (PC) is adopted as a carbon matrix to combine with RP to form PC@RP composites through a facile vaporization-condensation approach. The conductive porous carbon architecture improves the transfer of electron and Na⁺ in the composite. The robust carbon framework together with the chemical bonding between PC and RP effectively buffer the huge volumetric change of RP. As a result, the PC@RP composite material delivers a specific capacity of 655.1 mA h g^-1 at 0.1 A g^-1 with a capacity retention of 87% after 100 charging/discharging cycles. In particular, the full SIB assembled with P2-Na_2/3Ni_1/3Mn_1/3Ti_1/3O₂ as the cathode material and PC@RP as the anode material exhibits a specific capacity of 77.3 mA h g^-1 (based on the mass of cathode material) at 0.5 C, and 85% capacity is retained after 100 charging/discharging cycles.

Green in Situ Growth Solid Electrolyte Interphase Layer with High Rebound Resilience for Long-Life Lithium Metal Anodes

Lithium (Li) metal is one of the most promising anodes for the high-energy density lithium batteries. Nevertheless, it is still a great challenge to construct a dendrite-free Li anode with stable solid electrolyte interphase (SEI) by adopting environmentally friendly approaches. Herein, a green artificial Li polylactic acid (LiPLA) SEI layer with biodegradability and highly rebound resilience is fabricated via an in situ reaction to regulate Li metal plating/stripping behavior. Guided by this stable environmentally friendly LiPLA SEI, the Li anode shows excellent stability with suppressive dendrites as demonstrated by a stable cycling of 850 h in LiPLA-Li/LiPLA-Li symmetric batteries and a significant capacity retention rate enhancement of 18% in LiPLA-Li/LiFePO₄ full batteries and 25% in LiPLA-Li/LiNi_3/5Co_1/5-Mn_1/5O₂ full batteries. This proposed strategy provides a green and facile way to ameliorate the stability of the Li anode for safe and long-life lithium metal batteries.

Self-Healable Solid Polymeric Electrolytes for Stable and Flexible Lithium Metal Batteries

The key issue holding back the application of solid polymeric electrolytes in high-energy density lithium metal batteries is the contradictory requirements of high ion conductivity and mechanical stability. In this work, self-healable solid polymeric electrolytes (SHSPEs) with rigid-flexible backbones and high ion conductivity are synthesized by a facile condensation polymerization approach. The all-solid Li metal full batteries based on the SHSPEs possess freely bending flexibility and stable cycling performance as a result of the more disciplined metal Li plating/stripping, which have great implications as long-lifespan energy sources compatible with other wearable devices.

An Ordered Ni6 -Ring Superstructure Enables a Highly Stable Sodium Oxide Cathode

Sodium-based layered oxides are among the leading cathode candidates for sodium-ion batteries, toward potential grid energy storage, having large specific capacity, good ionic conductivity, and feasible synthesis. Despite their excellent prospects, the performance of layered intercalation materials is affected by both a phase transition induced by the gliding of the transition metal slabs and air-exposure degradation within the Na layers. Here, this problem is significantly mitigated by selecting two ions with very different MO bond energies to construct a highly ordered Ni₆ -ring superstructure within the transition metal layers in a model compound (NaNi_2/3 Sb_1/3 O₂ ). By virtue of substitution of 1/3 nickel with antimony in NaNiO₂ , the existence of these ordered Ni₆ -rings with super-exchange interaction to form a symmetric atomic configuration and degenerate electronic orbital in layered oxides can not only largely enhance their air stability and thermal stability, but also increase the redox potential and simplify the phase-transition process during battery cycling. The findings reveal that the ordered Ni₆ -ring superstructure is beneficial for constructing highly stable layered cathodes and calls for new paradigms for better design of layered materials.

High-Performance Lithiated SiOx Anode Obtained by a Controllable and Efficient Prelithiation Strategy

Silicon-based electrodes are promising and appealing for futuristic Li-ion batteries because of their high theoretical specific capacity. However, massive volume change of silicon upon lithiation and delithiation, accompanied by continual formation and destruction of the solid-electrolyte interface (SEI), leads to low Coulombic efficiency. Prelithiation of Si-based anode is regarded as an effective way for compensating for the loss of Li⁺ in the first discharging process. Here, a high-performance lithiated SiO_x anode was prepared by using a controllable, efficient, and novel prelithiation strategy. The lithiation of SiO_x is homogeneous and efficient in bulk due to well-improved Li⁺ diffusion in SiO_x. Moreover, the in situ formed SEI during the process of prelithiation reduces the irreversible capacity loss in the first cycle and thus improves the initial Coulombic efficiency (ICE). Half-cells and full cells based on the as-prepared lithiated SiO_x anode prominently increase the ICE from 79 to 89% and 68 to 87%, respectively. It is worth mentioning that the homogeneously lithiated SiO_x anode achieves stable 200 cycles in NCM622//SiO_x coin full cells. These exciting results provide applicable prospects of lithiated SiO_x anode in the next-generation high-energy-density Li-ion batteries.

Nonaqueous Sodium-Ion Full Cells: Status, Strategies, and Prospects

With ever-increasing efforts focused on basic research of sodium-ion batteries (SIBs) and growing energy demand, sodium-ion full cells (SIFCs), as unique bridging technology between sodium-ion half-cells (SIHCs) and commercial batteries, have attracted more and more interest and attention. To promote the development of SIFCs in a better way, it is essential to gain a systematic and profound insight into their key issues and research status. This Review mainly focuses on the interface issues, major challenges, and recent progresses in SIFCs based on diversified electrolytes (i.e., nonaqueous liquid electrolytes, quasi-solid-state electrolytes, and all-solid-state electrolytes) and summarizes the modification strategies to improve their electrochemical performance, including interface modification, cathode/anode matching, capacity ratio, electrolyte optimization, and sodium compensation. Outlooks and perspectives on the future research directions to build better SIFCs are also provided.

Air-Stable and High-Voltage Layered P3-Type Cathode for Sodium-Ion Full Battery

The development of highly efficient and stable cathodes for sodium-ion batteries (SIBs) is strategically critical to achieving large-scale electrical energy storage. Creating air-stable and high-voltage layered cathodes for sodium-ion full batteries still remains a challenge. Herein, we describe a rational design and preparation of a stable P3-Na_2/3Ni_1/4Mg_1/12Mn_2/3O₂ cathode. The cathode displays a satisfactory working voltage of 3.6 V and excellent cyclic stability over 100 cycles at a 1 C rate without obvious capacity fading. The results of ex situ X-ray diffraction (XRD) demonstrate that the P3-type structure is well retained even when charged to 4.4 V. Furthermore, the structural characterization by XRD Rietveld refinement, scanning electron microscopy, and electrochemical testing certifies that the cathode maintains its structure commendably even when soaked in water for 12 h. In particular, the P3- Na_2/3Ni_1/4Mg_1/12Mn_2/3O₂∥hard carbon full battery exhibits a desired competitively high voltage of 3.45 V and an attractive energy density of up to 412.2 W h kg^-1 based on the cathode. The comprehensive results achieved by the specially designed strategy provide guidance toward the exploration of stable cathodes in the application of SIBs as modern energy-storage devices.

Suppression of Monoclinic Phase Transitions of O3-Type Cathodes Based on Electronic Delocalization for Na-Ion Batteries

As high capacity cathodes, O3-type Na-based oxides always suffer from a series of monoclinic transitions upon sodiation/desodiation, mainly caused by Na⁺/vacancy ordering and Jahn-Teller (J-T) distortion, leading to rapid structural degradation and serious performance fading. Herein, a simple modulation strategy is proposed to address this issue based on refrainment of electron localization in expectation to alleviate the charge ordering and change of electronic structure, which always lead to Na⁺/vacancy ordering and J-T distortion, respectively. According to density functional theory calculations, Fe³⁺ with slightly larger radius is introduced into NaNi_0.5Mn_0.5O₂ with the intention of enlarging transition metal layers and facilitating electronic delocalization. The obtained NaFe_0.3Ni_0.35Mn_0.35O₂ exhibits a reversible phase transition of O3_hex-P3_hex without any monoclinic transitions in striking contrast with the complicated phase transitions (O3_hex-O'3_mon-P3_hex-P'3_mon-P3'_hex) of NaNi_0.5Mn_0.5O₂, thus excellently improving the capacity retention with a high rate kinetic. In addition, the strategy is also effective to enhance the air stability, proved by direct observation of atomic-scale ABF-STEM for the first time.

Engineering Janus Interfaces of Ceramic Electrolyte via Distinct Functional Polymers for Stable High-Voltage Li-Metal Batteries

The fast-ionic-conducting ceramic electrolyte is promising for next-generation high-energy-density Li-metal batteries, yet its application suffers from the high interfacial resistance and poor interfacial stability. In this study, the compatible solid-state electrolyte was designed by coating Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) with polyacrylonitrile (PAN) and polyethylene oxide (PEO) oppositely to satisfy deliberately the disparate interface demands. Wherein, the upper PAN constructs soft-contact with LiNi_0.6Mn_0.2Co_0.2O₂, and the lower PEO protects LATP from being reduced, guaranteeing high-voltage tolerance and improved stability toward Li-metal anode performed in one ceramic. Moreover, the core function of LATP is amplified to guide homogeneous ions distribution and hence suppresses the formation of a space-charge layer across interfaces, uncovered by the COMSOL Multiphysics concentration field simulation. Thus, such a bifunctional modified ceramic electrolyte integrates the respective superiority to render Li-metal batteries with excellent cycling stability (89% after 120 cycles), high Coulombic efficiency (exceeding 99.5% per cycle), and a dendrite-free Li anode at 60 °C, which represents an overall design of ceramic interface engineering for future practical solid battery systems.

MgSc2 Se4 -A Magnesium Solid Ionic Conductor for All-Solid-State Mg Batteries?

Recently, the ternary spinel selenide MgSc₂ Se₄ was proposed to have high magnesium ion mobility and is therefore an interesting potential candidate as a solid electrolyte in magnesium secondary batteries. To test the properties of the material, a modified solid-state reaction was used to synthesize pure MgSc₂ Se₄ . Electrochemical characterizations identified detrimental high electronic conductivities, which limit its application as a Mg-conducting solid electrolyte. Two methods were attempted to lower electronic conductivities, including the implementation of Se-rich phases and aliovalent doping, however, with no sufficient improvement. Based on the mixed conducting properties of MgSc₂ Se₄ , a reversible insertion/extraction of Mg²⁺ into the spinel structure could be demonstrated.

Nitriding-Interface-Regulated Lithium Plating Enables Flame-Retardant Electrolytes for High-Voltage Lithium Metal Batteries

Safety concerns are impeding the applications of lithium metal batteries. Flame-retardant electrolytes, such as organic phosphates electrolytes (OPEs), could intrinsically eliminate fire hazards and improve battery safety. However, OPEs show poor compatibility with Li metal though the exact reason has yet to be identified. Here, the lithium plating process in OPEs and Li/OPEs interface chemistry were investigated through ex situ and in situ techniques, and the cause for this incompatibility was revealed to be the highly resistive and inhomogeneous interfaces. Further, a nitriding interface strategy was proposed to ameliorate this issue and a Li metal anode with an improved Li cycling stability (300 h) and dendrite-free morphology is achieved. Meanwhile, the full batteries coupled with nickel-rich cathodes, such as LiNi_0.8 Co_0.1 Mn_0.1 O₂ , show excellent cycling stability and outstanding safety (passed the nail penetration test). This successful nitriding-interface strategy paves a new way to handle the incompatibility between electrode and electrolyte.

Unveiling the Role of Heteroatom Gradient-Distributed Carbon Fibers for Vanadium Redox Flow Batteries with Long Service Life

The fundamental understanding of electrocatalytic reaction process is anticipated to guide electrode upgradation and acquirement of high-performance vanadium redox flow batteries (VRFBs). Herein, a carbon fiber prototype system with a heteroatom gradient distribution has been developed with enlarged interlayer spacing and a high graphitization that improve the electronic conductivity and accelerate the electrocatalytic reaction, and the mechanism by which gradient-distributed heteroatoms enhance vanadium redox reactions was elucidated with the assistance of density functional theory calculations. All these contributions endow the obtained electrode prominent redox reversibility and durability with only 1.7% decay in energy efficiency over 1000 cycles at 150 mA cm^-2 in the VRFBs. Our work sheds light on the significance of elaborated electrode design and impels the in-depth investigation of VRFBs with long service life.

Extended Electrochemical Window of Solid Electrolytes via Heterogeneous Multilayered Structure for High-Voltage Lithium Metal Batteries

In response to the call for safer high-energy-density storage systems, high-voltage solid-state Li metal batteries have attracted extensive attention. Therefore, solid electrolytes are required to be stable against both Li anode and high-voltage cathodes; nevertheless, the requirements still cannot be completely satisfied. Herein, a heterogeneous multilayered solid electrolyte (HMSE) is proposed to broaden electrochemical window of solid electrolytes to 0-5 V, through different electrode/electrolyte interfaces to overcome the interfacial instability problems. Oxidation-resistance poly(acrylonitrile) (PAN) is in contact with the cathode, while reduction tolerant polyethylene glycol diacrylate contacts with Li metal anode. A Janus and flexible PAN@Li_1.4 Al_0.4 Ge_1.6 (PO₄ )₃ (80 wt%) composite electrolyte is designed as intermediate layer to inhibit dendrite penetration and ensure compact interface. Paired with LiNi_0.6 Co_0.2 Mn_0.2 O₂ and LiNi_0.8 Co_0.1 Mn_0.1 O₂ cathodes, which are rarely used in solid-state batteries, the solid-state Li metal batteries with HMSE exhibit excellent electrochemical performance including high capacity and long cycle life. Besides, the Li||Li symmetric batteries maintain a stable polarization less than 40 mV for more than 1000 h under 2 mA cm^-2 and effective inhibition of dendrite formation. This study offers a promising approach to extend the applications of solid electrolytes for high-voltage solid-state Li metal batteries.

Rational Design of Robust Si/C Microspheres for High-Tap-Density Anode Materials

Si has been recognized as a next-generation anode alternative to graphite for high-energy-density lithium-ion batteries. However, the most intractable problem of previous Si-based anodes is the relatively low compressive strength of particles because of excess voids and porous structures, thus leading to poor structural integrity and electrochemical performance under high pressure of the rolling procedure in practical application. Therefore, a rational design of robust Si/C microspheres with a compact nano/microstructure is an effective strategy to address the above-mentioned issues. In this ingenious structure, Si nanoparticles are homogeneously dispersed and anchored on flake graphite and then the composites self-assemble into microspheres via polycondensation and surface tension of pitch under high temperature and high pressure. Benefitting from this innovative approach and rational design, the obtained robust Si/C microspheres not only present high compressive property and high tap density (1.0 g cm^-3) but also demonstrate high initial Coulombic efficiency (90.5%) and cycling stability with areal capacity (4 mA h cm^-2) under a compaction density of 1.3 g cm^-3. Furthermore, the full cell assembled with LiNi_0.8Co_0.1Mn_0.1O₂ and the resultant Si/C microsphere anode also displays good cycling performance and rate capabilities. Owing to these aspects, the proposed rational design of encapsulating Si nanoparticles in high-tap-density microspheres could be extended to load other nanomaterials for advanced batteries.

Fungi-Enabled Synthesis of Ultrahigh-Surface-Area Porous Carbon

The growth of white-rot fungi is related to the superior infiltrability and biodegradability of hyphae on a lignocellulosic substrate. The superior biodegradability of fungi toward plant substrates affords tailored microstructures, which benefits subsequently high efficient carbonization and chemical activation. Here, the mechanism underlying the direct growth of mushrooms toward the lignocellulosic substrate is elucidated and a fungi-enabled method for the preparation of porous carbons with ultrahigh specific surface area (3439 m² g^-1 ) is developed. Such porous carbons could have potential applications in energy storage, environment treatment, and electrocatalysis. The present study reveals a novel pore formation mechanism in root-colonizing fungi and anticipates a valuable function for fungi in developing the useful porous carbons with a high specific surface area.

Phosphorus and oxygen co-doped composite electrode with hierarchical electronic and ionic mixed conducting networks for vanadium redox flow batteries

The GF-TCN electrodes with excellent electrocatalytic activity and faster electron/ion conduction indicate outstanding rate capability and energy efficiency of VRFBs.

Guiding Uniform Li Plating/Stripping through Lithium-Aluminum Alloying Medium for Long-Life Li Metal Batteries

The uncontrolled growth of Li dendrites upon cycling might result in low coulombic efficiency and severe safety hazards. Herein, a lithiophilic binary lithium-aluminum alloy layer, which was generated through an in situ electrochemical process, was utilized to guide the uniform metallic Li nucleation and growth, free from the formation of dendrites. Moreover, the formed LiAl alloy layer can function as a Li reservoir to compensate the irreversible Li loss, enabling long-term stability. The protected Li electrode shows superior cycling over 1700 h in a Li|Li symmetric cell.

Robust Electrodes with Maximized Spatial Catalysis for Vanadium Redox Flow Batteries

Catalytic efficiency is a crucial index for electrodes in flow batteries, and tremendous efforts have been devoted to exploring catalysts with as many reaction zones as possible. Nevertheless, the space between the reaction sites, especially for interstitial space utilization, is usually ignored and challengeable to exploit owing to the balance between the catalytic efficiency and structural stability. Herein, a three-dimensional conducting network was constructed via a nitrogen-rich carbon film-bridged graphite felt framework (GF@N-C) to maximize its electrocatalytic effectiveness toward redox species. As the electrode, GF@N-C exhibits a superior rate constant and catalytic efficiency at 370 mA cm^-2 and enables the vanadium redox flow battery to operate steadily at 200 mA cm^-2 with an energy efficiency of 74.3% and a discharge specific capacity of 23 A h L^-1. It is anticipated that the conducting network with optimized space utilization and catalysis will provide guidance for the design of high-efficiency electrodes and advance their development in flow batteries.

Advanced P2-Na2/3Ni1/3Mn7/12Fe1/12O2 Cathode Material with Suppressed P2-O2 Phase Transition toward High-Performance Sodium-Ion Battery

As a promising cathode material of sodium-ion battery, P2-type Na_2/3Ni_1/3Mn_2/3O₂ (NNMO) possesses a theoretically high capacity and working voltage to realize high energy storage density. However, it still suffers from poor cycling stability mainly incurred by the undesirable P2-O2 phase transition. Herein, the electrochemically active Fe³⁺ ions are introduced into the lattice of NNMO, forming Na_2/3Ni_1/3Mn_{2/3- x}Fe _xO₂ ( x = 0, 1/24, 1/12, 1/8, 1/6) to effectively stabilize the P2-type crystalline structure. In such Fe-substituted materials, both Ni²⁺/Ni⁴⁺ and Fe³⁺/Fe⁴⁺ couples take part in the redox reactions, and the P2-O2 phase transition is well restrained during cycling, as verified by ex situ X-ray diffraction. As a result, the optimized Na_2/3Ni_1/3Mn_7/12Fe_1/12O₂ (1/12-NNMF) has a long-term cycling stability with the fading rate of 0.05% per cycle over 300 cycles at 5 C. Furthermore, the 1/12-NNMF delivers excellent rate capabilities (65 mA h g^-1 at 25 C) and superior low-temperature performance (the capacity retention of 94% at -25 °C after 80 cycles) owing to the enhanced Na diffusion upon Fe doping, which is deduced by the studies of electrode kinetics. More significantly, the 1/12-NNMF also displays remarkable sodium-ion full-cell properties when merged with an LS-Sb@G anode, thus implying the possibility of their practical application.

Upgrading traditional liquid electrolyte via in situ gelation for future lithium metal batteries

High-energy lithium metal batteries (LMBs) are expected to play important roles in the next-generation energy storage systems. However, the uncontrolled Li dendrite growth in liquid electrolytes still impedes LMBs from authentic commercialization. Upgrading the traditional electrolyte system from liquid to solid and quasi-solid has therefore become a key issue for prospective LMBs. From this premise, it is particularly urgent to exploit facile strategies to accomplish this goal. We report that commercialized liquid electrolyte can be easily converted into a novel quasi-solid gel polymer electrolyte (GPE) via a simple and efficient in situ gelation strategy, which, in essence, is to use LiPF₆ to induce the cationic polymerization of the ether-based 1,3-dioxolane and 1,2-dimethoxyethane liquid electrolyte under ambient temperature. The newly developed GPE exhibits elevated protective effects on Li anodes and has universality for diversified cathodes including but not restricted to sulfur, olivine-type LiFePO₄, and layered LiNi_0.6Co_0.2Mn_0.2O₂, revealing tremendous potential in promoting the large-scale application of future LMBs.

Stable Sodium Storage of Red Phosphorus Anode Enabled by a Dual-Protection Strategy

Red phosphorus is appealing for anode use in sodium-ion batteries. However, the synthesis of electrochemically stable red P anodes remains challenging due to a notable volume variation upon (de)sodiation, and limited synthetic methods arising from the low ignition and sublimation temperatures. To address the above problems, we herein successfully develop an industrially adaptable process for scalable synthesis of affordable phosphorus/carbon (APC) anode materials with an excellent electrochemical performance at a significantly reduced cost. The key to our success is a delicately designed, self-organized, strongly interactive porous P/C structure filled with sodium alginate binder, which maintains the structural integrity of anode and enhances the electrical contact of red P upon its volume variation via a dual protection from porous structure and strong surface interactions. The APC anodes hence present ultrahigh initial Coulombic efficiency (86.2%), excellent cycling stability, and superior rate capability. The industrially adaptable process and excellent electrochemical performance endow the novel APC nano/microspheres with promising applications in high-performance Na-ion batteries.