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Anode‐free designs can obtain the ultimate energy density of lithium metal batteries. However, without a continuous Li supply from the anode side, it is much more challenging to achieve high capacity retention with a competitive energy density. Here, the lifespan of an anode‐free Li metal battery is prolonged by applying an epitaxial induced plating current‐collector (E‐Cu). The functional layer on E‐Cu initiates Li storage by an alloying approach, forming an epitaxial induce layer, which exhibits speedy surface diffusion for of Li‐ions, resulting in the block like epitaxial growth of Li. Moreover, this alloying process also promotes the formation of a LiF‐rich solid electrolyte interphase (SEI), which is very useful for uniform Li plating. Due to the benefits of epitaxial Li plating and LiF‐rich SEI, the initial coulombic efficiency of the E‐Cu/Li asymmetric cell increases from 93.24 to 98.24%, and the capacity retention of anode‐free NCM811/E‐Cu pouch cell increases from 66 to 84% with a remarkable energy density of 420 Wh kg−1 in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). This strategy is promising in the development of high energy batteries in extending their lifespans. [ABSTRACT FROM AUTHOR]

Solid-electrolyte interphase (SEI) is the key component that enables all advanced electrochemical devices, the best representative of which is Li-ion battery (LIB). It kinetically stabilizes electrolytes at potentials far beyond their thermodynamic stability limits, so that cell reactions could proceed reversibly. Its ad hoc chemistry and formation mechanism has been a topic under intensive investigation since the first commercialization of LIB 25 years ago. Traditionally SEI can only be formed in nonaqueous electrolytes. However, recent efforts successfully transplanted this concept into aqueous media, leading to significant expansion in the electrochemical stability window of aqueous electrolytes from 1.23 V to beyond 4.0 V. This not only made it possible to construct a series of high voltage/energy density aqueous LIBs with unprecedented safety, but also brought high flexibility and even "open configurations" that have been hitherto unavailable for any LIB chemistries. While this new class of aqueous electrolytes has been successfully demonstrated to support diversified battery chemistries, the chemistry and formation mechanism of the key component, an aqueous SEI, has remained virtually unknown. In this work, combining various spectroscopic, electrochemical and computational techniques, we rigorously examined this new interphase, and comprehensively characterized its chemical composition, microstructure and stability in battery environment. A dynamic picture obtained reveals how a dense and protective interphase forms on anode surface under competitive decompositions of salt anion, dissolved ambient gases and water molecule. By establishing basic laws governing the successful formation of an aqueous SEI, the in-depth understanding presented in this work will assist the efforts in tailor-designing better interphases that enable more energetic chemistries operating farther away from equilibria in aqueous media. [ABSTRACT FROM AUTHOR]

Narrow electrochemical stability window (1.23 V) of aqueous electrolytes is always considered the key obstacle preventing aqueous sodium-ion chemistry of practical energy density and cycle life. The sodium-ion water-in-salt electrolyte (NaWiSE) eliminates this barrier by offering a 2.5 V window through suppressing hydrogen evolution on anode with the formation of a Na+-conducting solid-electrolyte interphase (SEI) and reducing the overall electrochemical activity of water on cathode. A full aqueous Na-ion battery constructed on Na0.66[Mn0.66Ti0.34]O2 as cathode and NaTi2(PO4)3 as anode exhibits superior performance at both low and high rates, as exemplified by extraordinarily high Coulombic efficiency (>99.2%) at a low rate (0.2 C) for >350 cycles, and excellent cycling stability with negligible capacity losses (0.006% per cycle) at a high rate (1 C) for >1200 cycles. Molecular modeling reveals some key differences between Li-ion and Na-ion WiSE, and identifies a more pronounced ion aggregation with frequent contacts between the sodium cation and fluorine of anion in the latter as one main factor responsible for the formation of a dense SEI at lower salt concentration than its Li cousin. [ABSTRACT FROM AUTHOR]

High electrochemical reversibility of the TiS 2 anode in “Water-in-Salt” electrolyte (21 m LiTFSI in H 2 O) is demonstrated for the first time. The wide electrochemical window and low chemical activity of H 2 O in the “Water-in-Salt” electrolyte not only significantly enhanced the electrochemical reversibility of TiS 2 but also effectively suppressed the hydrolysis side reaction in the aqueous electrolyte. Paired with a LiMn 2 O 4 cathode, the LiMn 2 O 4 /TiS 2 full cell delivers a relatively high discharge voltage of 1.7 V and an energy density of 78 Wh kg − 1 as well as a satisfactory rate performance. [ABSTRACT FROM AUTHOR]

A 2.9 V intrinsic safe aqueous LiNi0.5Mn1.5O4/Mo6S8 full cell delivers 80 W h kg−1 energy density with capacity decay of 0.075% per cycle (5 C). After the electrolyte pH value adjustment, almost full capacity of LiNi0.5Mn1.5O4 (125 mA h kg−1) is achieved, and 126 W h kg−1 energy density is provided for LiNi0.5Mn1.5O4/Mo6S8 cell, representing one of the highest voltage and energy density among all the aqueous batteries. [ABSTRACT FROM AUTHOR]

A new super-concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra-high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO2 as the anode material, and a 2.5 V aqueous Li-ion cell based on LiMn2O4 and carbon-coated TiO2 delivered the unprecedented energy density of 100 Wh kg−1 for rechargeable aqueous Li-ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the 'water-in-salt' electrolyte further pushed the energy densities of aqueous Li-ion cells closer to those of the state-of-the-art Li-ion batteries. [ABSTRACT FROM AUTHOR]

A new super-concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra-high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO2 as the anode material, and a 2.5 V aqueous Li-ion cell based on LiMn2O4 and carbon-coated TiO2 delivered the unprecedented energy density of 100 Wh kg−1 for rechargeable aqueous Li-ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the 'water-in-salt' electrolyte further pushed the energy densities of aqueous Li-ion cells closer to those of the state-of-the-art Li-ion batteries. [ABSTRACT FROM AUTHOR]

We demonstrate for the first time that by simply substituting ether-based electrolyte (1.0 M NaCF 3 SO 3 in diglyme) for the commonly used carbonate-based electrolyte, the cyclability of FeS 2 towards sodium storage can be significantly improved. A sodiation capacity over 600 mAh/g and a discharge energy density higher than 750 Wh/kg are obtained for FeS 2 at 20 mA/g. When tested at 60 mA/g, FeS 2 presents a sodiation capacity of 530 mAh/g and retains 450 mAh/g after 100 cycles, much better than the cycling performance of Na/FeS 2 tested in carbonate-based electrolyte. [ABSTRACT FROM AUTHOR]

Solid electrolyte interphase (SEI) makes the electrochemical window of aqueous electrolytes beyond the thermodynamics limitation of water. However, achieving the energetic and robust SEI is more challenging in aqueous electrolytes because the low SEI formation efficiency (SFE) only contributed from anion‐reduced products, and the low SEI formation quality (SFQ) negatively impacted by the hydrogen evolution, resulting in a high Li loss to compensate for SEI formation. Herein, we propose a highly efficient strategy to construct Spatially‐Temporally Synchronized (STS) robust SEI by the involvement of synergistic chemical precipitation‐electrochemical reduction. In this case, a robust Li3PO4‐rich SEI enables intelligent inherent growth at the active site of the hydrogen by the chemical capture of the OH− stemmed from the HER to trigger the ionization balance of dihydrogen phosphate (H2PO4−) shift to insoluble solid Li3PO4. It is worth highlighting that the Li3PO4 formation does not extra‐consume lithium derived from the cathode but makes good use of the product of HER (OH−), prompting the SEI to achieve 100 % SFE and pushing the HER potential into −1.8 V vs. Ag/AgCl. This energetic and robust SEI offers a new way to achieve anion/concentration‐independent interfacial chemistry for the aqueous batteries. [ABSTRACT FROM AUTHOR]

Solid electrolyte interphase (SEI) makes the electrochemical window of aqueous electrolytes beyond the thermodynamics limitation of water. However, achieving the energetic and robust SEI is more challenging in aqueous electrolytes because the low SEI formation efficiency (SFE) only contributed from anion‐reduced products, and the low SEI formation quality (SFQ) negatively impacted by the hydrogen evolution, resulting in a high Li loss to compensate for SEI formation. Herein, we propose a highly efficient strategy to construct Spatially‐Temporally Synchronized (STS) robust SEI by the involvement of synergistic chemical precipitation‐electrochemical reduction. In this case, a robust Li3PO4‐rich SEI enables intelligent inherent growth at the active site of the hydrogen by the chemical capture of the OH− stemmed from the HER to trigger the ionization balance of dihydrogen phosphate (H2PO4−) shift to insoluble solid Li3PO4. It is worth highlighting that the Li3PO4 formation does not extra‐consume lithium derived from the cathode but makes good use of the product of HER (OH−), prompting the SEI to achieve 100 % SFE and pushing the HER potential into −1.8 V vs. Ag/AgCl. This energetic and robust SEI offers a new way to achieve anion/concentration‐independent interfacial chemistry for the aqueous batteries. [ABSTRACT FROM AUTHOR]

Highly concentrated aqueous solutions of LiN(SO2CF3)2 (5-20 M at 25 °C) are used as an electrolyte in a CR2032-type coin cell containing either LiMn2O4 or LiNi0.8Co0.15Al0.05O2 as the cathode and Cu-leached Mo6S8 Chevrel phase as the anode separated by glass fiber fabrics. [ABSTRACT FROM AUTHOR]

The desperate pursuit of high gravimetric specific energy leads to the ignorance of volumetric energy density that is one of the basic requirements for batteries. Due to the high volumetric capacity, less‐prone formation of dendrite, and low reduction potential of Mg metal, rechargeable Mg batteries are considered with innately high volumetric energy density. Nevertheless, the substantial elevation in energy density is compromised by extremely excessive Mg metal anode. Herein, the proof‐of‐concept of anode‐free Mg2Mo6S8‐MgS/Cu batteries is proposed, in which MgS as the premagnesiation additive constantly decomposes to replenish Mg loss by electrolyte corrosion over cycling, while both Mg2Mo6S8 and MgS acts as the active material to reversibly provide high capacities. Besides, Mg2Mo6S8 shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode‐free Mg2Mo6S8‐MgS/Cu batteries deliver a high reversible capacity of 190 mAh g−1 with the capacity retention of 92% after 100 cycles, corresponding to the highly competitive energy density of 420 Wh L−1. The proposed anode‐free Mg battery here spotlights the great promise of Mg batteries in achieving high volumetric energy densities, which will significantly expedite the advances of Mg batteries in practice. [ABSTRACT FROM AUTHOR]

Aqueous Li‐ion batteries (ALIBs) are safe, environmentally friendly, and cost‐effective, promising for electric energy storage (EES). The high voltage ALIBs (HV‐ALIBs) supported by water‐in‐salt electrolytes are ideal for lowering the energy cost ($/Wh) of EES. However, HV‐ALIBs have been built with a high positive/negative capacity ratio (P/N ratio) to ensure their long‐term cycle life due to the irreversible Li consumption in the initial cycle induced by the solid electrolyte interface (SEI) formation and the parasitic reaction. Thus, the benefits of HV‐ALIBs in cost and energy density are mitigated inevitably. Generally, the feasible approach is adding per‐lithiation additives (PAs) to compensate for the capacity loss in the initial cycle. However, using PAs in ALIBs is challenging due to the high chemical activity of water. Here, a new strategy to achieve the pre‐lithiation by introducing manganese metal as a sacrificial PA for HV‐ALIBs that can provide over 900 mAh g−1 specific capacity without any adverse impact is proposed. The P/N ratio reduces to 1.02 by the LiMn2O4||TiO2 pouch cell using the sacrificial manganese PA. This results in a high initial energy density above 120 Wh kg−1 and outstanding cycle stability with a capacity retention of 80% after 400 cycles. [ABSTRACT FROM AUTHOR]

The LiFePO4/FePO4 phase transition process is remarkable in terms of its excellent reversibility, making this redox system extremely promising for high rate lithium storage. The recent observation of ordering effects (Li0.5FePO4) during the phase transition challenges the traditional two phase models. In this work, the phenomenon of staging for LiFePO4 for different sizes (70 nm and 50 nm) by high resolution aberration corrected annular bright electron microscopy is detected, investigated, and discussed along with previous results on larger crystals. In the small crystals, staging is found throughout with a decrease of order from center to the surface. For the larger crystal, a staging phase occurs constituting the interfacial zone (width around 15 nm) between LiFePO4 and FePO4. A comparison is made to recent experiments on even larger crystals showing such an interphase of smaller extent (around 2 nm). Thus it appears that these zones narrow with increasing size. These findings are discussed in the light of phase transition thermodynamics and kinetics. In particular, the possibility is discussed that the staging interphase may constitute a low energy solution to the LiFePO4/FePO4 contact. [ABSTRACT FROM AUTHOR]

The high weight fraction of the electrolyte in lithium–sulfur (Li–S) full cell is the primary reason its specific energy is much below expectations. Thus far, it is still a challenge to reduce the electrolyte volume of Li–S batteries owing to their high cathode porosity and electrolyte depletion from the Li metal anode. Herein, we propose an ultralight electrolyte (0.83 g mL−1) by introducing a weakly‐coordinating and Li‐compatible monoether, which greatly reduces the weight fraction of electrolyte within the whole cell and also enables Li–S pouch cell functionality under lean‐electrolyte conditions. Compared to Li–S batteries using conventional counterparts (≈1.2 g mL−1), the Li–S pouch cells equipped with our ultralight electrolyte could achieve an ultralow electrolyte weight/capacity ratio (E/C) of 2.2 g Ah−1 and realize a 19.2 % improvement in specific energy (from 329.9 to 393.4 Wh kg−1) under E/S=3.0 μL mg−1. Moreover, more than 20 % improvement in specific energy could be achieved using our ultralight electrolyte at various E/S ratios. [ABSTRACT FROM AUTHOR]

The high weight fraction of the electrolyte in lithium–sulfur (Li–S) full cell is the primary reason its specific energy is much below expectations. Thus far, it is still a challenge to reduce the electrolyte volume of Li–S batteries owing to their high cathode porosity and electrolyte depletion from the Li metal anode. Herein, we propose an ultralight electrolyte (0.83 g mL−1) by introducing a weakly‐coordinating and Li‐compatible monoether, which greatly reduces the weight fraction of electrolyte within the whole cell and also enables Li–S pouch cell functionality under lean‐electrolyte conditions. Compared to Li–S batteries using conventional counterparts (≈1.2 g mL−1), the Li–S pouch cells equipped with our ultralight electrolyte could achieve an ultralow electrolyte weight/capacity ratio (E/C) of 2.2 g Ah−1 and realize a 19.2 % improvement in specific energy (from 329.9 to 393.4 Wh kg−1) under E/S=3.0 μL mg−1. Moreover, more than 20 % improvement in specific energy could be achieved using our ultralight electrolyte at various E/S ratios. [ABSTRACT FROM AUTHOR]

Anode‐free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal‐based batteries. Here, we prolong the lifespan of an anode‐free Li metal battery by introducing Li‐rich Li2[Ni0.8Co0.1Mn0.1]O2 into the cathode as a Li‐ions extender. The Li2[Ni0.8Co0.1Mn0.1]O2 can release a large amount of Li‐ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li‐rich cathode and high reversibility of Li metal on Cu foil, the anode‐free pouch cells enable to achieve 447 Wh kg−1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). [ABSTRACT FROM AUTHOR]

Anode‐free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal‐based batteries. Here, we prolong the lifespan of an anode‐free Li metal battery by introducing Li‐rich Li2[Ni0.8Co0.1Mn0.1]O2 into the cathode as a Li‐ions extender. The Li2[Ni0.8Co0.1Mn0.1]O2 can release a large amount of Li‐ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li‐rich cathode and high reversibility of Li metal on Cu foil, the anode‐free pouch cells enable to achieve 447 Wh kg−1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). [ABSTRACT FROM AUTHOR]

Mass dissolution is one main problems for cathodes in aqueous electrolytes due to the strong polarity of water molecules. In principle, mass dissolution is a thermodynamically favorable process as determined by the Gibbs free energy. However, in real situations, dissolution kinetics, which include viscosity, dissolving mass mobility, and interface properties, are also a critical factor influencing the dissolution rate. Both thermodynamic and kinetic dissolving factors can be regulated by the ratio of salt to solvent in the electrolyte. In this study, concentration‐controlled cathode dissolution is investigated in a susceptible Na3V2(PO4)3 cathode whose time‐, cycle‐, and state‐of‐charge‐dependent dissolubility are evaluated by multiple electrochemical and chemical methods. It is verified that the super‐highly concentrated water‐in‐salt electrolyte has a high viscosity, low vanadium ion diffusion, low polarity of solvated water, and scarce solute−water dissolving surfaces. These factors significantly lower the thermodynamic‐controlled solubility and the dissolving kinetics via time and physical space local mass interfacial confinement, thereby inducing a new mechanism of interface concentrated‐confinement which improves the cycling stability in real aqueous rechargeable sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

The lack of high‐power and stable cathodes prohibits the development of rechargeable metal (Na, Mg, Al) batteries. Herein, poly(hexaazatrinaphthalene) (PHATN), an environmentally benign, abundant and sustainable polymer, is employed as a universal cathode material for these batteries. In Na‐ion batteries (NIBs), PHATN delivers a reversible capacity of 220 mAh g−1 at 50 mA g−1, corresponding to the energy density of 440 Wh kg−1, and still retains 100 mAh g−1 at 10 Ag−1 after 50 000 cycles, which is among the best performances in NIBs. Such an exceptional performance is also observed in more challenging Mg and Al batteries. PHATN retains reversible capacities of 110 mAh g−1 after 200 cycles in Mg batteries and 92 mAh g−1 after 100 cycles in Al batteries. DFT calculations, X‐ray photoelectron spectroscopy, Raman, and FTIR show that the electron‐deficient pyrazine sites in PHATN are the redox centers to reversibly react with metal ions. [ABSTRACT FROM AUTHOR]

The lack of high‐power and stable cathodes prohibits the development of rechargeable metal (Na, Mg, Al) batteries. Herein, poly(hexaazatrinaphthalene) (PHATN), an environmentally benign, abundant and sustainable polymer, is employed as a universal cathode material for these batteries. In Na‐ion batteries (NIBs), PHATN delivers a reversible capacity of 220 mAh g−1 at 50 mA g−1, corresponding to the energy density of 440 Wh kg−1, and still retains 100 mAh g−1 at 10 Ag−1 after 50 000 cycles, which is among the best performances in NIBs. Such an exceptional performance is also observed in more challenging Mg and Al batteries. PHATN retains reversible capacities of 110 mAh g−1 after 200 cycles in Mg batteries and 92 mAh g−1 after 100 cycles in Al batteries. DFT calculations, X‐ray photoelectron spectroscopy, Raman, and FTIR show that the electron‐deficient pyrazine sites in PHATN are the redox centers to reversibly react with metal ions. [ABSTRACT FROM AUTHOR]

Abstract Transition metal sulfides with hierarchical (ball in ball) micro/nanoporous structures have drawn wide spread interests for various applications, such as energy storage, catalysis, solar cells, owing to their unique features and intriguing properties. However, precise control of synthesizing process for hierarchical porous nanospheres of transition metal sulfides remains a big challenge. In addition, the charging and discharging process of transition metal sulfides in electrochemical storage is still a black box. Herein we design and precise control of synthesizing a transition metal sulfide with hierarchical porous nanosphere structure, namely cobalt sulfide hierarchical porous nanospheres (HPNs). Brownian snowball mechanism is put forward to explain the formation mechanism of CoS samples, which is supported by first-principles calculations. The proposed Brownian snowball mechanism helps us understand the formation process and facilitates comprehensive and precise manipulation, a key requirement for industrial scale-up. The CoS hierarchical porous nanospheres with a specific surface area of approximately 140 m2/g possess a total specific capacitance of 1310 F/g and 932 F/g at a current density of 5 A/g when used as electrode materials for electrochemical capacitors. The capacitance reflected hybrid electrical energy storage and is separated into double layer charging and the Faradaic contribution from the OH− ions reactions with surface atoms. It is demonstrated that Faradaic capacitance dominates in CoS hierarchical porous nanospheres exceeding 770 F/g by an analysis of the voltammetric sweep data. Graphical abstract Image 1 Highlights • Precise control of synthesizing process for cobalt sulfide hierarchical porous nanospheres. • Brownian snowball mechanism is put forward and supported by first-principles calculations. • The capacitance reflects hybrid electrical energy storage. • Largely improved EC performance could be attributed to the unique architecture. [ABSTRACT FROM AUTHOR]

Abstract: Sodium (Na) is one of the more abundant elements on earth and exhibits similar chemical properties as lithium (Li), indicating that Na could be applied to a similar battery system. Like aqueous Li‐ion batteries, aqueous sodium‐ion batteries (ASIBs) are also demonstrated to be one of the most promising stationary power sources for sustainable energies such as wind and solar power. Compared to traditional nonaqueous batteries, ASIBs may solve the safety problems associated with the highly toxic and flammable organic electrolyte in the traditional lithium‐ion and sodium‐ion batteries. During the past decades, many efforts are made to improve the performance of the ASIBs. The present review focuses on the latest advances in the exploration and development of ASIB systems and related components, including cathodes, anodes, and electrolytes. Previously reported studies are briefly summarized, together with the presentation of new findings based on the electrochemical performance, cycling stability, and morphology approaches. In addition, the main opportunities, achievements, and challenges in this field are briefly commented and discussed. [ABSTRACT FROM AUTHOR]

Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite-free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg−1) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlS x. Herein, we demonstrate the first reversible Al/S battery in ionic-liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid-state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid-state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system. [ABSTRACT FROM AUTHOR]

Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite-free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg−1) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlS x. Herein, we demonstrate the first reversible Al/S battery in ionic-liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid-state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid-state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system. [ABSTRACT FROM AUTHOR]

Transition metal fluorides (such as FeF 3 and FeF 2 ) based on conversion chemistry have been considered as a promising alternative to the intercalation cathode materials due to the high capacity and high energy density. However, the critical challenges for these materials come from the absence of Li source in them, and low power density and poor cycling stability. Herein, pre-lithiated FeF 3 with extremely small size of Fe and LiF nanoparticles (both ∼6 nm) homogeneously embedded in the carbon matrix were synthesized using a facile and scalable in situ strategy. Benefited from the ultra-small Fe and LiF nanoparticles, uniform distribution, and intimate contact between the active species and the carbon matrix, the particle-to-particle interfacial resistance and diffusion length for Li and F are dramatically reduced. As a result, a high specific capacity of over 400 mA h g −1 with a discharge energy density of ∼700 W h kg −1 and favorable cycling performance are achieved, making such composite a promising high-capacity cathode for LIBs. Furthermore, the built-in Li source in this composite renders it a drop-in replacement for cathode materials used in the current LIB configurations, thus paving the way for the practical applications in the next generation of high energy density LIBs. [ABSTRACT FROM AUTHOR]

A SnP3 anode material with a theoretical volumetric capacity of 6890 mAh cm−3 is investigated for Na‐ion batteries. The SnP3/C can deliver a reversible capacity of 810 mAh g−1 at a current density of 150 mA g−1 for 150 cycles. The superior performance is attributed to the strong bonding interaction of P and Sn after desodiation. [ABSTRACT FROM AUTHOR]

A rechargeable hybrid Mg2+/Li+ battery is designed by coupling a dendrite‐free magnesium anode with an electrolyte‐compatible cathode in a mixed Mg2+/Li+ electrolyte. Due to the highly reversible lithiation/delithiation of the cathode and Mg deposition/dissolution in the electrolyte, the battery demonstrates the best overall performance among reported magnesium‐ion batteries and mixed‐ion batteries in terms of cycling stability, specific capacity, specific energy, and rate capability. [ABSTRACT FROM AUTHOR]