Ultralight Electrolyte with Protective Encapsulation Solvation Structure Enables Hybrid Sulfur-Based Primary Batteries Exceeding 660 Wh/kg.

An electrochemical couple of lithium and sulfur possesses the highest theoretical energy density (>2600 Wh/kg) at the material level. However, disappointingly, it is out of place in primary batteries due to its low accessible energy density at the cell level (≤500 Wh/kg) and poor storage performance. Herein, a low-density methyl tert-butyl ether was tailored for an ultralight electrolyte (0.837 g/mL) with a protective encapsulation solvation structure which reduced electrolyte weight (23.1%), increased the utilization of capacity (38.1%), and simultaneously forfended self-discharge. Furthermore, active fluorinated graphite partially replaced inactive carbon to construct a hybrid sulfur-based cathode to bring the potential energy density into full play. Our demonstrated pouch cell achieved an incredible energy density of 661 Wh/kg with a negligible self-discharge rate based on the above innovations. Our work is anticipated to provide a new direction to realize the practicality of lithium-sulfur primary batteries.

Development of High-Performance Iron-Based Phosphate Cathodes toward Practical Na-Ion Batteries.

Iron-based phosphate cathode of Na4Fe3(PO4)2(P2O7) has been regarded as a low-cost and structurally stable cathode material for Na-ion batteries (NIBs). However, their practical application is greatly hindered by the insufficient electrochemical performance and limited energy density. Here, we report a new iron-based phosphate cathode of Na4.5Fe3.5(PO4)2.5(P2O7) with the intergrown heterostructure of the maricite-type NaFePO4 and orthorhombic Na4Fe3(PO4)2(P2O7) phases at a mole ratio of 0.5:1. Benefited from the increased composition ratio and the spontaneous activation of the maricite-type NaFePO4 phase, the as-prepared Na4.5Fe3.5(PO4)2.5(P2O7) composites deliver a reversible capacity over 130 mA h g-1 and energy density close to 400 W h kg-1, which is far beyond that of the single-phase Na4Fe3(PO4)2(P2O7) cathode (∼120 mA h g-1 and ∼350 W h kg-1). Moreover, the kg-level products from the scale-up synthesis demonstrate a stable cycling performance over 2000 times at 3 C in pouch cells. We believe that our findings could show the way forward the practical application of the iron-based phosphate cathodes for NIBs.

Dendrite-Free Dual-Phase Li-Ba Alloy Anode Enabled by Ordered Array of Built-in Mixed Conducting Microchannels.

The development and application of lithium (Li) anode is hindered by volumetric variation, dendritic Li growth, and parasitic reactions. Herein, a dual-phase Li-barium (Ba) alloy with self-assembled microchannels array is synthesized through a one-step thermal fusion method to investigate the inhibition effect of lithiophilic composite porous array on Li dendrites. The Li-rich Li-Ba alloy (BaLi24) as composite Li electrode exhibits an ordered porous structure of BaLi4 intermetallic compound after delithiation, which acts as a built-in 3D current collector during Li plating/striping process. Furthermore, the lithiophilic BaLi4 alloy scaffold is a mixed conductor, featuring with Li+ ions diffusion capability, which can efficiently transport the reduced Li to the interior of the electrode structure. This unique top-down growth mode can effectively prohibit Li dendrites growth and improve the space utilization of 3D electrode structure. The spin-polarized density functional theory (DFT) calculations suggest that the absorption capability of BaLi4 benefits the deposition of Li metal. As a result, the cell performance with the dual-phase Li-Ba alloy anode is significantly improved.

Tailoring Electronic Structure to Achieve Maximum Utilization of Transition Metal Redox for High-Entropy Na Layered Oxide Cathodes.

Charge compensation from cationic and anionic redox couples accompanying Na+ (de)intercalation in layered oxide cathodes contributes to high specific capacity. However, the engagement level of different redox couples remains unclear and their relationship with Na+ content is less studied. Here we discover that it is possible to take full advantage of the high-voltage transition metal (TM) redox reaction through low-valence cation substitution to tailor the electronic structure, which involves an increased ratio of Na+ content to available charge transfer number of TMs. Taking NaxCu0.11Ni0.11Fe0.3Mn0.48O2 as the example, the Li+ substitution increases the ratio to facilitate the high-voltage TM redox activity, and further F-ion substitution decreases the covalency of the TM-O bond to relieve structural changes. As a consequence, the final high-entropy Na0.95Li0.07Cu0.11Ni0.11Fe0.3Mn0.41O1.97F0.03 cathode demonstrates ∼29% capacity increase contributed by the high-voltage TMs and exhibits excellent long-term cycling stability due to the improved structural reversibility. This work provides a paradigm for the design of high-energy-density electrodes by simultaneous electronic and crystal structure modulation.

Unraveling the Reaction Mystery of Li and Na with Dry Air.

Li and Na metals with high energy density are promising in application in rechargeable batteries but suffer from degradation in the ambient atmosphere. The phenomenon that in terms of kinetics, Li is stable but Na is unstable in dry air has not been fully understood. Here, we use in situ environmental transmission electron microscopy combined with theoretical simulations and reveal that the different stabilities in dry air for Li and Na are reflected by the formation of compact Li2O layers on Li metal, while porous and rough Na2O/Na2O2 layers on Na metal are a consequence of the different thermodynamic and kinetics in O2. It is shown that a preformed carbonate layer can change the kinetics of Na toward an anticorrosive behavior. Our study provides a deeper understanding of the often-overlooked chemical reactions with environmental gases and enhances the electrochemical performance of Li and Na by controlling interfacial stability.

Surface Engineering Stabilizes Rhombohedral Sodium Manganese Hexacyanoferrates for High-Energy Na-Ion Batteries.

The rhombohedral sodium manganese hexacyanoferrate (MnHCF) only containing cheap Fe and Mn metals was regarded as a scalable, low-cost, and high-energy cathode material for Na-ion batteries. However, the unexpected Jahn-teller effect and significant phase transformation would cause Mn dissolution and anisotropic volume change, thus leading to capacity loss and structural instability. Here we report a simple room-temperature route to construct a magical Cox B skin on the surface of MnHCF. Benefited from the complete coverage and the buffer effect of Cox B layer, the modified MnHCF cathode exhibits suppressed Mn dissolution and reduced intergranular cracks inside particles, thereby demonstrating thousands-cycle level cycling lifespan. By comparing two key parameters in the real energy world, i.e., cost per kilowatt-hours and cost per cycle-life, our developed Cox B coated MnHCF cathode demonstrates more competitive application potential than the benchmarking LiFePO4 for Li-ion batteries.

Using High-Entropy Configuration Strategy to Design Na-Ion Layered Oxide Cathodes with Superior Electrochemical Performance and Thermal Stability.

Na-ion layered oxide cathodes (NaxTMO2, TM = transition metal ion(s)), as an analogue of lithium layered oxide cathodes (such as LiCoO2, LiNixCoyMn1-x-yO2), have received growing attention with the development of Na-ion batteries. However, due to the larger Na+ radius and stronger Na+-Na+ electrostatic repulsion in NaO2 slabs, some undesired phase transitions are observed in NaxTMO2. Herein, we report a high-entropy configuration strategy for NaxTMO2 cathode materials, in which multicomponent TMO2 slabs with enlarged interlayer spacing help strengthen the whole skeleton structure of layered oxides through mitigating Jahn-Teller distortion, Na+/vacancy ordering, and lattice parameter changes. The strengthened skeleton structure with a modulated particle morphology dramatically improves the Na+ transport kinetics and suppresses intragranular fatigue cracks and TM dissolution, thus leading to highly improved performances. Furthermore, the elaborate high-entropy TMO2 slabs enhance the TM-O bonding energy to restrain oxygen release and thermal runaway, benefiting for the improvement of thermal safety.

[Formulation regularity of traditional Chinese medicine in treatment of sinusitis based on data mining].

Based on the Drugdataexpy and the prescription modern application database, this study explored the formulation regularity of ancient and modern prescriptions for the treatment of sinusitis. The Chinese medicinal prescriptions for the treatment of sinusitis with various syndromes were retrieved from the above databases and the corresponding formulation regularity was investigated by frequency analysis, association rule analysis, and factor analysis. Eighty-seven Chinese medicinal prescriptions were included, involving five syndrome types of sinusitis and 160 Chinese medicine, which were mainly effective in releasing exterior, clearing heat, and tonifying deficiency, and acted on the lung meridian due to cold and warm nature and pungent and bitter flavor or on the spleen meridian due to warm nature and pungent flavor. Seventeen core Chinese medicine were screened out by topological data analysis, including Angelicae Dahuricae Radix, Magnoliae Flos, Glycyrrhizae Radix et Rhizoma, Xanthii Fructus, and Scutellariae Radix. Chinese medicine such as Magnoliae Flos, Angelicae Dahuricae Radix, and Xanthii Fructus were commonly used in the treatment of sinusitis of wind-heat in the lung meridian, while the combination of Glycyrrhizae Radix et Rhizoma, Magnoliae Flos, Angelicae Dahuricae Radix, Chuanxiong Rhizoma, etc. was the key compatibility in treating sinusitis of dampness-heat in the spleen and stomach. Six common factors were extracted from the factor analysis of the above two syndrome types. The findings indicate that the exterior-releasing, heat-clearing, and deficiency-tonifying Chinese medicine with cold and warm nature and pungent flavor are preferential options for the clinical treatment of sinusitis. Treatment should be based on syndrome differentiation and key therapeutic principles should be followed.

Screening Heteroatom Configurations for Reversible Sloping Capacity Promises High-Power Na-Ion Batteries.

Heteroatom doping has been proved to effectively enhance the sloping capacity, nevertheless, the high sloping capacity almost encounters a conflict with the disappointing initial Coulombic efficiency (ICE). Herein, we propose a heteroatom configuration screening strategy by introducing a secondary carbonization process for the phosphate-treated carbons to remove the irreversible heteroatom configurations but with the reversible ones and free radicals remaining, achieving a simultaneity between the high sloping capacity and ICE (≈250 mAh g-1 and 80 %). The Na storage mechanism was also studied based on this "slope-dominated" carbon to reveal the reason for the absence of the plateau. This work could inspire to distinguish and filter the irreversible heteroatom configurations and facilitate the future design of practical "slope-dominated" carbon anodes towards high-power Na-ion batteries.

Joint Cationic and Anionic Redox Chemistry for Advanced Mg Batteries.

Lack of appropriate cathodes severely restrains the development of high-energy Mg batteries. In this work, we proposed joint cationic and anionic redox chemistry of transition-metal (TM) sulfides as the most promising way out. A series of solid-solution pyrite FexCo1-xS2 (0 ≤ x ≤ 1) was specially designed, in which S 3p electrons pour into the d bands of Fe and Co, generating redox-active dimerized (S2)2-. The Fe0.5Co0.5S2 sample is highlighted to deliver a high specific energy of 240 Wh/kg at room temperature involving both cationic (Fe and Co) and anionic (S) redox. The highly delocalized electronic clouds in pyrite structures comfortably accommodate the charge of Mg2+, contributing to the fast kinetics and the superior cycling stability of the Fe0.5Co0.5S2. It is anticipated that the joint cationic and anionic redox chemistry proposed in this work would be the ultimate answer for designing high-energy cathodes for advanced Mg batteries.

Li-Rich Li2 [Ni0.8 Co0.1 Mn0.1 ]O2 for Anode-Free Lithium Metal Batteries.

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 [Ni0.8 Co0.1 Mn0.1 ]O2 into the cathode as a Li-ions extender. The Li2 [Ni0.8 Co0.1 Mn0.1 ]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 ).

Ultralight Electrolyte for High-Energy Lithium-Sulfur Pouch Cells.

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.

Revealing High Na-Content P2-Type Layered Oxides as Advanced Sodium-Ion Cathodes.

Layered Na-based oxides with the general composition of NaxTMO2 (TM: transition metal) have attracted significant attention for their high compositional diversity that provides tunable electrochemical performance for electrodes in sodium-ion batteries. The various compositions bring forward complex structural chemistry that is decisive for the layered stacking structure, Na-ion conductivity, and the redox activity, potentially promising new avenues in functional material properties. In this work, we have explored the maximum Na content in P2-type layered oxides and discovered that the high-content Na in the host enhances the structural stability; moreover, it promotes the oxidation of low-valent cations to their high oxidation states (in this case Ni2+). This can be rationalized by the increased hybridization of the O(2p)-TM(3d-eg*) states, affecting both the local TM environment as well as the interactions between the NaO2 and TMO2 layers. These properties are highly beneficial for the Na storage capabilities as required for cathode materials in sodium-ion batteries. It leads to excellent Na-ion mobility, a large storage capacity (>100 mAh g-1 between 2.0-4.0 V), yet preventing the detrimental sliding of the TMO2 layers (P2-O2 structural transition), as reflected by the ultralong cycle life (3000 (dis)charge cycles demonstrated). These findings expand the horizons of high Na-content P2-type materials, providing new insights of the electronic and structural chemistry for advanced cathode materials.

Intercalation chemistry of graphite: alkali metal ions and beyond.

Reversibly intercalating ions into host materials for electrochemical energy storage is the essence of the working principle of rocking-chair type batteries. The most relevant example is the graphite anode for rechargeable Li-ion batteries which has been commercialized in 1991 and still represents the benchmark anode in Li-ion batteries 30 years later. Learning from past lessons on alkali metal intercalation in graphite, recent breakthroughs in sodium and potassium intercalation in graphite have been demonstrated for Na-ion batteries and K-ion batteries. Interestingly, some significant differences proved to exist for the intercalation of Na+ and K+ into graphite compared with the Li+ case. Such different host-guest interactions are unique depending on the host materials and electrolytes, which greatly contribute to a deeper understanding of intercalation-type electrode materials for next generation alkali metal ion batteries. This review summarizes significant advances from both experimental and theoretical calculations with a focus on comparing the intercalation of three alkali metal ions (Li+, Na+, K+) into graphite and aims to clarify the intimate host-guest relationships and the underlying mechanisms. New approaches developed to achieve favorable intercalation coupled with the challenges in this field are also discussed. We also extrapolate alkali metal ion intercalation in graphite to mono-/multi-valent ions in layered electrode materials, which will deepen the understanding of intercalation chemistry and provide guidance to explore new guests and hosts.

High-Entropy Layered Oxide Cathodes for Sodium-Ion Batteries.

Material innovation on high-performance Na-ion cathodes and the corresponding understanding of structural chemistry still remain a challenge. Herein, we report a new concept of high-entropy strategy to design layered oxide cathodes for Na-ion batteries. An example of layered O3-type NaNi0.12 Cu0.12 Mg0.12 Fe0.15 Co0.15 Mn0.1 Ti0.1 Sn0.1 Sb0.04 O2 has been demonstrated, which exhibits the longer cycling stability (ca. 83 % of capacity retention after 500 cycles) and the outstanding rate capability (ca. 80 % of capacity retention at the rate of 5.0 C). A highly reversible phase-transition behavior between O3 and P3 structures occurs during the charge-discharge process, and importantly, this behavior is delayed with more than 60 % of the total capacity being stored in O3-type region. Possible mechanism can be attributed to the multiple transition-metal components in this high-entropy material which can accommodate the changes of local interactions during Na+ (de)intercalation. This strategy opens new insights into the development of advanced cathode materials.

Ionic liquids and derived materials for lithium and sodium batteries.

The ever-growing demand for advanced energy storage devices in portable electronics, electric vehicles and large scale power grids has triggered intensive research efforts over the past decade on lithium and sodium batteries. The key to improve their electrochemical performance and enhance the service safety lies in the development of advanced electrode, electrolyte, and auxiliary materials. Ionic liquids (ILs) are liquids consisting entirely of ions near room temperature, and are characterized by many unique properties such as ultralow volatility, high ionic conductivity, good thermal stability, low flammability, a wide electrochemical window, and tunable polarity and basicity/acidity. These properties create the possibilities of designing batteries with excellent safety, high energy/power density and long-term stability, and also provide better ways to synthesize known materials. IL-derived materials, such as poly(ionic liquids), ionogels and IL-tethered nanoparticles, retain most of the characteristics of ILs while being endowed with other favourable features, and thus they have received a great deal of attention as well. This review provides a comprehensive review of the various applications of ILs and derived materials in lithium and sodium batteries including Li/Na-ion, dual-ion, Li/Na-S and Li/Na-air (O2) batteries, with a particular emphasis on recent advances in the literature. Their unique characteristics enable them to serve as advanced resources, medium, or ingredient for almost all the components of batteries, including electrodes, liquid electrolytes, solid electrolytes, artificial solid-electrolyte interphases, and current collectors. Some thoughts on the emerging challenges and opportunities are also presented in this review for further development.

Revealing an Interconnected Interfacial Layer in Solid-State Polymer Sodium Batteries.

Replacing the commonly used nonaqueous liquid electrolytes in rechargeable sodium batteries with polymer solid electrolytes is expected to provide new opportunities to develop safer batteries with higher energy densities. However, this poses challenges related to the interface between the Na-metal anode and polymer electrolytes. Driven by systematically investigating the interface properties, an improved interface is established between a composite Na/C metal anode and electrolyte. The observed chemical bonding between carbon matrix of anode with solid polymer electrolyte, prevents delamination, and leads to more homogeneous plating and stripping, which reduces/suppresses dendrite formation. Full solid-state polymer Na-metal batteries, using a high mass loaded Na3 V2 (PO4 )3 cathode, exhibit ultrahigh capacity retention of more than 92 % after 2 000 cycles and over 80 % after 5 000 cycles, as well as the outstanding rate capability.

Slope-Dominated Carbon Anode with High Specific Capacity and Superior Rate Capability for High Safety Na-Ion Batteries.

The comprehensive performance of carbon anodes for Na-ion batteries (NIBs) is largely restricted by their inferior rate capability and safety issues. Herein, a slope-dominated carbon anode is achieved at a low temperature of 800 °C, which delivers a high reversible capacity of 263 mA h g-1 at 0.15C with an impressive initial Coulombic efficiency (ICE) of 80 %. When paired with the NaNi1/3 Fe1/3 Mn1/3 O2 cathode, the reversible capacity at 6C is still 75 % of that at 0.15C, and 73 % of the capacity is retained after 1000 cycles at 3C. The enhanced Na storage performance could be attributed to the unique microstructure with randomly oriented short carbon layers and the relatively higher defect concentration. Given its robustness, such a low-temperature carbonization strategy could also be applicable to other precursors and provide a new opportunity to design slope-dominated carbon anodes for high safety, low-cost NIBs with excellent ICE and superior rate capability.

An O3-type Oxide with Low Sodium Content as the Phase-Transition-Free Anode for Sodium-Ion Batteries.

Layered transition metal oxides Nax MO2 (M=transition metal) with P2 or O3 structure have attracted attention in sodium-ion batteries (NIBs). A universal law is found to distinguish structural competition between P2 and O3 types based on the ratio of interlayer distances of the alkali metal layer d(O-Na-O) and transition-metal layer d(O-M-O) . The ratio of about 1.62 can be used as an indicator. O3-type Na0.66 Mg0.34 Ti0.66 O2 oxide is prepared as a stable anode for NIBs, in which the low Na-content (ca. 0.66) usually undergoes a P2-type structure with respect to Nax MO2 . This material delivers an available capacity of about 98 mAh g-1 within a voltage range of 0.4-2.0 V and exhibits a better cycling stability (ca. 94.2 % of capacity retention after 128 cycles). In situ X-ray diffraction reveals a single-phase reaction in the discharge-charge process, which is different from the common phase transitions reported in O3-type electrodes, ensuring long-term cycling stability.

In Situ Atomic-Scale Observation of Electrochemical Delithiation Induced Structure Evolution of LiCoO2 Cathode in a Working All-Solid-State Battery.

We report a method for in situ atomic-scale observation of electrochemical delithiation in a working all-solid-state battery using a state-of-the-art chip based in situ transmission electron microscopy (TEM) holder and focused ion beam milling to prepare an all-solid-state lithium-ion battery sample. A battery consisting of LiCoO2 cathode, LLZO solid state electrolyte and gold anode was constructed, delithiated and observed in an aberration corrected scanning transmission electron microscope at atomic scale. We found that the pristine single crystal LiCoO2 became nanosized polycrystal connected by coherent twin boundaries and antiphase domain boundaries after high voltage delithiation. This is different from liquid electrolyte batteries, where a series of phase transitions take place at LiCoO2 cathode during delithiation. Both grain boundaries become more energy favorable along with extraction of lithium ions through theoretical calculation. We also proposed a lithium migration pathway before and after polycrystallization. This new methodology could stimulate atomic scale in situ scanning/TEM studies of battery materials and provide important mechanistic insight for designing better all-solid-state battery.