Understanding the Coupling Mechanism of Intercalation and Conversion Hybrid Storage in Lithium-Graphite Anode.

Anodes with high capacity and long lifespan play an important role in the advanced batteries. However, none of the existing anodes can meet these two requirements simultaneously. Lithium (Li)-graphite composite anode presents great potential in balancing these two requirements. Herein, the working mechanism of Li-graphite composite anode is comprehensively investigated. The capacity decay features of the composite anode are different from those of Li ion intercalation in Li ion batteries and Li metal deposition in Li metal batteries. An intercalation and conversion hybrid storage mechanism are proposed by analyzing the capacity decay ratios in the composite anode with different initial specific capacities. The capacity decay models can be divided into four stages including Capacity Retention Stage, Relatively Independent Operation Stage, Intercalation & Conversion Coupling Stage, Pure Li Intercalation Stage. When the specific capacity is between 340 and 450 mAh g-1, its capacity decay ratio is between that of pure intercalation and conversion model. These results intensify the comprehensive understandings on the working principles in Li-graphite composite anode and present novel insights in the design of high-capacity and long-lifespan anode materials for the next-generation batteries.

Light-Assisted Lithium Metal Anode Enabled by In Situ Photoelectrochemical Engineering.

Rechargeable battery devices with high energy density are highly demanded by the modern society. The use of lithium (Li) anodes is extremely attractive for future rechargeable battery devices. However, the notorious Li dendritic and instability of solid electrolyte interface (SEI) issues pose series of challenge for metal anodes. Here, based on the inspiration of in situ photoelectrochemical engineering, it is showed that a tailor-made composite photoanodes with good photoelectrochemical properties (Li affinity property and photocatalytic property) can significantly improve the electrochemical deposition behavior of Li anodes. The light-assisted Li anode is accommodated in the tailor-made current collector without uncontrollable Li dendrites. The as-prepared light-assisted Li metal anode can achieve the in situ stabilization of SEI layer under illumination. The corresponding in situ formation mechanism and photocatalytic mechanism of composite photoanodes are systematically investigated via DFT theoretical calculation, ex situ UV-vis and ex situ XPS characterization. It is worth mentioning that the as-prepared composite photoanodes can adapt to the ultra-high current density of 15 mA cm-2 and the cycle capacity of 15 mAh cm-2 under light, showing no dendritic morphology and low hysteresis voltage. This work is of great significance for the commercialization of new generation Li metal batteries.

Photoelectrochemical Engineering for Light-Assisted Rechargeable Metal Batteries: Mechanism, Development, and Future.

Rechargeable battery devices with high energy density are highly demanded by  our  modern society. The use of metal anodes is extremely attractive for future rechargeable battery devices. However, the notorious metal dendritic and instability of solid electrolyte interface issues pose a series of challenges for metal anodes. Recently, considering the indigestible dynamical behavior of metal anodes, photoelectrochemical engineering of light-assisted metal anodes have been rapidly developed since they efficiently utilize the integration and synergy of oriented crystal engineering and photocatalysis engineering, which provided a potential way to unlock the interface electrochemical mechanism and deposition reaction kinetics of metal anodes. This review starts with the fundamentals of photoelectrochemical engineering and follows with the state-of-art advance of photoelectrochemical engineering for light-assisted rechargeable metal batteries where photoelectrode materials, working principles, types, and practical applications are explained. The last section summarizes the major challenges and some invigorating perspectives for future research on light-assisted rechargeable metal batteries.

Computational-Guided Design of Photoelectrode Active Materials for Light-Assisted Energy Storage.

The design of a novel photoelectric integrated system is considered to be an efficient way to utilize and store inexhaustible solar energy. However, the mechanism of photoelectrode under illuminate conditions is still unclear. Density functional theory (DFT) provides standardized analysis and becomes a powerful way to explain the photoelectrochemical mechanism. Herein, the feasibility of four metal oxide configurations as photoelectrode materials by using a high throughput calculation method based on DFT are investigated. According to the photoelectrochemical properties, band structure and density of states are calculated, and the intercalate/deintercalate simulation is performed with adsorption configuration. The calculation indicates that the band gap of Fe2 CoO4 (2.404 eV) is narrower than that of Co3 O4 (2.553 eV), as well as stronger adsorption energy (-3.293 eV). The relationship between the electronic structure and the photoelectrochemical performance is analyzed and verified according to the predicted DFT results by subsequent experiments. Results show that the Fe2 CoO4 photoelectrode samples exhibit higher coulombic efficiency (97.4%) than that under dark conditions (94.9%), which is consistent with the DFT results. This work provides a general method for the design of integrated photoelectrode materials and is expected to be enlightening for the adjustment of light-assisted properties of multifunctional materials.

Engineering Oxygen Vacancies on VO2 Multilayered Structures for Efficient Zn2+ Storage.

Vanadium dioxide (VO2 (B)) is a proper cathode for aqueous zinc-ion batteries (ZIBs) due to its shear structure and high theoretical capacity. However, the sluggish kinetics and structure instability derived from the strong electrostatic interaction between Zn2+ and the VO2 host hinder its further application. Defect engineering is a useful way to circumvent the limitations. Herein, oxygen-defect VO2 (Od -VO2 ) with tunable oxygen vacancy concentration are obtained via a facile one-step hydrothermal method by adjusting ascorbic acid addition. It is proved that oxygen vacancies can provide extra active sites for Zn2+ storage and reduced electrostatic barrier for Zn2+ transportation, but excessive vacancy content would lead to a reverse effect. The Od -VO2 cathode with optimum oxygen vacancy concentration achieves an outstanding performance with a high capacity of 380 mAhg-1 at 0.2 A g-1 , excellent cycle stability with 92.6 % capacity retention after 2000 cycles at 3 A g-1 and a high energy density of 197 Wh kg-1 at the power density of 0.641 kW kg-1 . Therefore, this defect engineering method for Od -VO2 provides an attractive way for high-performance aqueous ZIB cathodes.

Achieving High Performance Electrode for Energy Storage with Advanced Prussian Blue-Drived Nanocomposites-A Review.

Recently, Prussian blue analogues (PBAs)-based anode materials (oxides, sulfides, selenides, phosphides, borides, and carbides) have been extensively investigated in the field of energy conversion and storage. This is due to PBAs' unique properties, including high theoretical specific capacity, environmental friendly, and low cost. We thoroughly discussed the formation of PBAs in conjunction with other materials. The performance of composite materials improves the electrochemical performance of its energy storage materials. Furthermore, new insights are provided for the manufacture of low-cost, high-capacity, and long-life battery materials in order to solve the difficulties in different electrode materials, combined with advanced manufacturing technology and principles. Finally, PBAs and their composites' future challenges and opportunities are discussed.

Advance of Prussian Blue-Derived Nanohybrids in Energy Storage: Current Status and Perspective.

Great changes have occurred in the energy storage area in recent years as a result of rapid economic expansion. People have conducted substantial research on sustainable energy conversion and storage systems in order to mitigate the looming energy crisis. As a result, developing energy storage materials is critical. Materials with an open frame structure are known as Prussian blue analogs (PBAs). Anode materials for oxides, sulfides, selenides, phosphides, borides, and carbides have been extensively explored as anode materials in the field of energy conversion and storage in recent years. The advantages and disadvantages of oxides, sulfides, selenides, phosphides, borides, carbides, and other elements, as well as experimental methodologies and electrochemical properties, are discussed in this work. The findings reveal that employing oxides, sulfides, selenides, phosphides, borides, and other electrode materials to overcome the problems of low conductivity, excessive material loss, and low specific volume is ineffective. Therefore, this review intends to address the issues of diverse energy storage materials by combining multiple technologies to manufacture battery materials with low cost, large capacity, and extended service life.

A Photo-rechargeable Aqueous Zinc-Tellurium Battery Enabled by the Janus-Jointed Perovskite/Te Photocathode.

The combination of photo-driven self-powered supplies and energy storage systems is considered as a promising candidate to solve the global energy dilemma. The photo-absorber and the energy storage material are integrated into the photocathode to effectively achieve a high-energy and high-efficiency energy system. In this work, we report the customized Janus-jointed photocathode design (integrating with highly efficient halide perovskite and tellurium composite electrode) and introduce it into the aqueous zinc-tellurium battery. The well-matched energy level of the Janus-jointed photocathode ensures the conversion of the photoenergy into electrical energy by transferring the photoexcited charge between each. As expected, in the photo-assisted recharging model, the decreased 0.1 V charge voltage and the extra 362 mA h g-1 at 100 mA g-1 demonstrated the significant merits of saving energy for such a photo-rechargeable Zn-Te (PRZT) battery. When the current density is 1000 mA g-1, the specific capacity of the prepared photocathode is 83% higher than that under dark conditions. More importantly, the photogenerated charge by the perovskite under light illumination could also directly photocharge the battery with no external current, indicating the self-powering traits. The rational design in this work is believed to provide a sustainable mode for efficient charging of the aqueous PRZT battery.

ZnTe/rGO Composite as the Fully Zinced Conversion-Type Cathodes for Aqueous Zinc Ion Batteries.

Conversion-type cathodes for aqueous zinc ion batteries (ZIBs) can provide flat plateau slop and stable output potential, compared to general intercalation-type cathodes. The high volumetric capacity and stable output potential of Te make it a promising cathode for ZIBs, but sluggish kinetics and large volume change hinder its further application. To address these issues, we revisit fully zinced ZnTe and construct ZnTe/rGO composites as the new conversion-type cathode. The electrode undergoes a solid-to-solid conversion reaction and shows a stable output potential with ultra-flat discharge plateau slop of 0.09 V (Ah g-1 )-1 . When ZnTe is de-zinced and transformed to Te during charge process, it has a volume shrinkage which generates empty space in graphene matrix for latter volume expansion of Te. The graphene matrix also improves conductivity and reaction kinetics of the cathode. Due to the combination of pre-zincation of ZnTe, graphene matrix and the elimination of "shuttle effects" process, ZnTe/rGO electrode exhibits a high and stable capacity of 186 mAh g-1 at 500 mA g-1 after 300 cycling, with almost no decay after initial 10 cycles.

Photoassisted High-Performance Lithium Anode Enabled by Oriented Crystal Planes.

Lithium (Li) metal anodes are candidates for the next-generation high-performance lithium-ion batteries (LIBs). However, uncontrolable Li dendrite growth leads to safety issues and a low Coulombic efficiency (CE), which hinders the commercialization of Li metal batteries. Stable Li anodes based on the tailored plane deposition and photoassisted synergistic current collectors are currently the subject of research; however, there are few related studies. To suppress the growth of Li dendrites and achieve dense Li deposition, we design a low-cost customized-facet/photoassisted synergistic dendrite-free anode. The tailored (002) plane endows it with a nanorod array/microsphere composite structure and exhibits a strong affinity for Li, which effectively reduces the Li+ nucleation overpotential and promotes uniform Li deposition. Notably, during the photoassisted Li deposition/stripping process, due to electron-hole separation, a weakly charged layer is formed on the (002) surface and local charge carrier changes are induced, reducing the overpotential by 8.3 mV, enhancing the reaction kinetics, and resulting in a high CE of ∼99.3% for the 300th cycle at 2 mA cm-2. This work is of great significance for the field of next-generation photoassisted Li metal anodes.

Interface Crystallographic Optimization of Crystal Plane for Stable Metallic Lithium Anode.

Li metal, the ideal anode material for rechargeable batteries, suffers from the inherent limitations of uneven interface kinetics and dendrite growth. Herein, we tackle this issue by applying an interface crystallographic optimization strategy. We demonstrate a promising metallic Li anode design by introducing a customized magnetron sputtering layer of preferred orientation copper coating on the surface of a current collector. The sputtered Cu layer employed is stable against the highly reactive robust Li metal to render the surface lithiophilic and achieve promoted interface kinetics due to the perfect interface-crystal plane matching between the sputtered copper layer and premier Li metal. The dendrite-free Li anode sustains stable interface kinetics and achieves a stable life span of 200 cycles during the plating and stripping process in commercial carbonate electrolytes. This design based on crystallographic optimization provides important insights into the design principles of the Li metal anode as well as other alkali metal anodes (Na, K, Zn, Mg, and Al).

Integrated Photovoltaic Charging and Energy Storage Systems: Mechanism, Optimization, and Future.

As an emerging solar energy utilization technology, solar redox batteries (SPRBs) combine the superior advantages of photoelectrochemical (PEC) devices and redox batteries and are considered as alternative candidates for large-scale solar energy capture, conversion, and storage. In this review, a systematic summary from three aspects, including: dye sensitizers, PEC properties, and photoelectronic integrated systems, based on the characteristics of rechargeable batteries and the advantages of photovoltaic technology, is presented. The matching problem of high-performance dye sensitizers, strategies to improve the performance of photoelectrode PEC, and the working mechanism and structure design of multienergy photoelectronic integrated devices are mainly introduced and analyzed. In particular, the devices and improvement strategies of high-performance electrode materials are analyzed from the perspective of different photoelectronic integrated devices (liquid-based and solid-state-based). Finally, future perspectives are provided for further improving the performance of SPRBs. This work will open up new prospects for the development of high-efficiency photoelectronic integrated batteries.

Element-Doped Mxenes: Mechanism, Synthesis, and Applications.

Heteroatom doping can endow MXenes with various new or improved electromagnetic, physicochemical, optical, and structural properties. This greatly extends the arsenal of MXenes materials and their potential for a spectrum of applications. This article comprehensively and critically discusses the syntheses, properties, and emerging applications of the growing family of heteroatom-doped MXenes materials. First, the doping strategies, synthesis methods, and theoretical simulations of high-performance MXenes materials are summarized. In order to achieve high-performance MXenes materials, the mechanism of atomic element doping from three aspects of lattice optimization, functional substitution, and interface modification is analyzed and summarized, aiming to provide clues for developing new and controllable synthetic routes. The mechanisms underlying their advantageous uses for energy storage, catalysis, sensors, environmental purification and biomedicine are highlighted. Finally, future opportunities and challenges for the study and application of multifunctional high-performance MXenes are presented. This work could open up new prospects for the development of high-performance MXenes.

Nanoscale interface engineering of inorganic Solid-State electrolytes for High-Performance alkali metal batteries.

All-solid-state metal batteries (ASSMBs) have been regarded as the ideal candidate for the next-generation high-energy storage system due to their ultrahigh specific capacity and the lowest redox potential. However, the uncontrollable chemical reactivity during cycling which directly determines the growth behaviour of metal dendrites, the low coulombic efficiency and the safety concerns severely limit their real-world applications.. Crystallographic optimization based on solid-state electrolytes (SSEs) provides an atomic-scale and fundamental solution for the inhibition of dendrite growth in metal anodes, which has attracted widespread attentions. From this perspective, we summarize the recent advance of the crystallographic optimization for various classes of solid-state electrolytes. We highlight the recent experimental findings of crystallographic optimization for a new generation of all-solid-state batteries, including lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, with the aim of providing a deeper understanding of the crystallographic reactions in ASSMBs. The challenges and prospects for the future design and engineering of crystallographic optimization of SSEs are discussed, providing ideas for further research into crystallographic optimization to improve the performance of rechargeable batteries.

Porous Heteroatom-Doped Ti3C2Tx MXene Microspheres Enable Strong Adsorption of Sodium Polysulfides for Long-Life Room-Temperature Sodium-Sulfur Batteries.

The practical application of Na-S batteries is largely hindered by their low mass loading, inferior rate capability, and poor cycling performance. Herein, we report a design strategy for encapsulation of sodium polysulfides using Ti3C2Tx MXene. Porous nitrogen-doped Ti3C2Tx MXene microspheres have been synthesized by a facile synthesis method. Porous nitrogen-doped Ti3C2Tx MXene microspheres contain abundant pore structures and heteroatom functional groups for structural and chemical synergistic encapsulation of sodium polysulfides. Sodium-sulfur batteries, based on the as-proposed cathode, demonstrated outstanding electrochemical performances, including a high reversible capacity (980 mAh g-1 at 0.5 C rate) and extended cycling stability (450.1 mAh g-1 at 2 C after 1000 cycles at a high areal sulfur loading of 5.5 mg cm-2). This MXene-based hybrid material is a promising cathode host material for polysulfide-retention, enabling high-performance Na-S batteries.

Boosting Performance of Na-S Batteries Using Sulfur-Doped Ti3C2Tx MXene Nanosheets with a Strong Affinity to Sodium Polysulfides.

Sodium-sulfur batteries using abundant elements offer an attractive alternative to currently used batteries, but they need better sulfur host materials to compete with lithium-ion batteries in capacity and cyclability. We report an in situ sulfur-doping strategy to functionalize MXene nanosheets by introducing heteroatomic sulfur into the MXene structure form the MAX phase precursor. By employing the vacuum freeze-drying method, a three-dimensional (3D) wrinkled MXene nanoarchitecture with the high specific surface area was prepared. The tailor-made wrinkled sulfur-doped MXene (S-Ti3C2Tx) nanosheets were applied as an electrode host material in room temperature sodium-sulfur batteries. The S-Ti3C2Tx matrix shows high polarity with sodium polysulfides, restricting the diffusion of sodium polysulfides. The MXene/sulfur electrode can achieve high areal sulfur loading up to 4.5 mg cm-2 as well as good electrochemical performance (reversible capacity of 577 mAh g-1 at 2 C after 500 cycles).

Two-Dimensional Arrays of Transition Metal Nitride Nanocrystals.

The synthesis of low-dimensional transition metal nitride (TMN) nanomaterials is developing rapidly, as their fundamental properties, such as high electrical conductivity, lead to many important applications. However, TMN nanostructures synthesized by traditional strategies do not allow for maximum conductivity and accessibility of active sites simultaneously, which is a crucial factor for many applications in plasmonics, energy storage, sensing, and so on. Unique interconnected two-dimensional (2D) arrays of few-nanometer TMN nanocrystals not only having electronic conductivity in-plane, but also allowing transport of ions and electrolyte through the porous nanosheets, which are obtained by topochemical synthesis on the surface of a salt template, are reported. As a demonstration of their application in a lithium-sulfur battery, it is shown that 2D arrays of several nitrides can achieve a high initial capacity of >1000 mAh g-1 at 0.2 C and only about 13% degradation over 1000 cycles at 1 C under a high areal sulfur loading (>5 mg cm-2 ).

Triclinic Off-Stoichiometric Na3.12Mn2.44(P2O7)2/C Cathode Materials for High-Energy/Power Sodium-Ion Batteries.

The application of sodium-ion batteries (SIBs) requires a suitable cathode material with low cost, nontoxic, high safety, and high energy density, which is still a big challenge; thus, a basic research on exploring new types of materials is imperative. In this work, a manganic pyrophosphate and carbon compound Na3.12Mn2.44(P2O7)2/C has been synthesized through a feasible sol-gel method. Rietveld refinement reveals that Na3.12Mn2.44(P2O7)2 adopts a triclinic structure ( P1̅ space group), which possesses spacious ion diffusion channels for facile sodium migration. The off-stoichiometric phase is able to offer more reversible Na+, delivering an enhanced reversible capacity of 114 mA h g-1 at 0.1 C, and because of the strong "inductive effect" that (P2O7)4- groups imposing on the Mn3+/Mn2+ redox couple, Na3.12Mn2.44(P2O7)2/C presents high platforms above 3.6 V, contributing a remarkable energy density of 376 W h kg-1, which is among the highest Fe-/Mn-based polyanion-type cathode materials. Furthermore, the off-stoichiometric compound also presents satisfactory rate capability and long-cycle stability, with a capacity retention of 75% after 500 cycles at 5 C. Ex situ X-ray diffraction demonstrates a single-phase reaction mechanism, and the density functional theory calculations display two one-dimensional sodium migration paths with low energy barriers in Na3.12Mn2.44(P2O7)2, which is vital for the facile sodium storage. We believe that this compound will be a competitive cathode material for large-scale SIBs.

Highly Efficient, Cost Effective, and Safe Sodiation Agent for High-Performance Sodium-Ion Batteries.

The development of sodium-ion batteries has been hindered so far by the large irreversible capacity of hard carbon anodes and other anode materials in the initial few cycles, as sodium ions coming from cathode materials is consumed in the formation of the solid-electrolyte interface (SEI) and irreversibly trapped in anodes. Herein, the successful synthesis of an environmentally benign and cost-effective sodium salt (Na2 C4 O4 ) is reported that could be applied as additive in cathodes to solve the irreversible-capacity issues of anodes in sodium-ion batteries. When added to Na3 (VO)2 (PO4 )2 F cathode, the cathode delivered a highly stable capacity of 135 mAh g-1 and stable cycling performance. The water-stable Na3 (VO)2 (PO4 )2 F cathode in combination with a water-soluble sacrificial salt eliminates the need for using any toxic solvents for laminate preparation, thus paving way for greener electrode fabrication techniques. A 100 % increase in capacity of sodium cells (full-cell configuration) has been observed when using the new sodium salt at a C-rate of 2C. Regardless of the electrode fabrication technique, this new salt finds use in both aqueous and non-aqueous cathode-fabrication techniques for sodium-ion batteries.

Confined Sulfur in 3 D MXene/Reduced Graphene Oxide Hybrid Nanosheets for Lithium-Sulfur Battery.

Three-dimensional metal carbide MXene/reduced graphene oxide hybrid nanosheets are prepared and applied as a cathode host material for lithium-sulfur batteries. The composite cathodes are obtained through a facile and effective two-step liquid-phase impregnation method. Owing to the unique 3 D layer structure and functional 2 D surfaces of MXene and reduced graphene oxide nanosheets for effective trapping of sulfur and lithium polysulfides, the MXene/reduced graphene oxide/sulfur composite cathodes deliver a high initial capacity of 1144.2 mAh g-1 at 0.5 C and a high level of capacity retention of 878.4 mAh g-1 after 300 cycles. It is demonstrated that hybrid metal carbide MXene/reduced graphene oxide nanosheets could be a promising cathode host material for lithium-sulfur batteries.