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The preferentially selective extraction of Li

Na-ion layered oxide cathodes (Na

Room-temperature Na-ion batteries have attracted great interest for over a decade owing to their natural abundance and similar intercalation chemistry with Li-ion. However, due to the uncontrolled decomposition of electrolyte and formation of solid electrolyte interphase, the large majority of sodium anode materials exhibit extremely low initial Coulombic efficiency and unsatisfactory cycling stability. Here we introduce a novel layered material, P2-Na0.547[Mg0.25Mn0.75]O2, as an SEI-free negative electrode. This material, delivers a reversible capacity of 126 mAh g−1 with a high initial Coulombic efficiency of 108%, and capacity retention of ∼ 80% after 1000 cycles at 4C rate. Pairing with Na3V2(PO4)3 cathode, excellent rate performance of ∼ 60% capability at 15C, and extra-high initial Coulombic efficiency of 97% are achieved, all attributed to the SEI-free feature of Na0.547[Mg0.25Mn0.75]O2. These results demonstrate the practical potential of our SEI-free anode material for high-power and long-life Na-ion batteries.

Solid-state batteries offering both high energy density and safety have aroused widespread interest as promising power sources for electric vehicles. However, the interfacial mechanical stability of inorganic electrolyte is inferior to that of organic electrolytes and the high stack pressure (several to hundreds of megapascals) is required to maintain the intimate contact with electrodes. Here we report a class of inorganic glass solid electrolytes with polymer-like viscoelasticity, which possess both advantages of inorganic and polymer electrolytes and can enable pressure-less Li- and Na-based solid-state batteries (< 0.1 MPa). These electrolytes are synthesized by simply replacing chlorine of tetrachloroaluminates with oxygen, demonstrating high ionic conductivity of ~1 mS cm-1 at 30℃ for both Li+ and Na+. They can also exhibit superior chemo-mechanical compatibility with 4.3 V cathodes without additional stack pressure. Moreover, the inorganic glass solid electrolytes are feasible for scale-up, not only enabling to be made into thin films through a rolling process owing to its polymer-like flexibility but also facilitating the complete infiltration of the electrode materials like a liquid battery due to the low melting temperature below 160℃. We believe that these viscoelastic inorganic solid electrolytes will inspire us to design new solid electrolytes and accelerate practical application of pressure-less solid-state batteries.

Aggressive chemistry involving Li metal anode (LMA) and high-voltage LiNi0.8Mn0.1Co0.1O2 (NCM811) cathode is deemed as a pragmatic approach to pursue the desperate 400 Wh kg−1. Yet, their implementation is plagued by low Coulombic efficiency and inferior cycling stability. Herein, we propose an optimally fluorinated linear carboxylic ester (ethyl 3,3,3-trifluoropropanoate, FEP) paired with weakly solvating fluoroethylene carbonate and dissociated lithium salts (LiBF4 and LiDFOB) to prepare a weakly solvating and dissociated electrolyte. An anion-enrichment interface prompts more anions’ decomposition in the inner Helmholtz plane and higher reduction potential of anions. Consequently, the anion-derived interface chemistry contributes to the compact and columnar-structure Li deposits with a high CE of 98.7% and stable cycling of 4.6 V NCM811 and LiCoO2 cathode. Accordingly, industrial anode-free pouch cells under harsh testing conditions deliver a high energy of 442.5 Wh kg−1 with 80% capacity retention after 100 cycles.

The air-sensitivity of transition metal oxide cathode materials (Na

We rationally designed and fabricated F-doped NTO with the morphology of hollow spheres (F-NTO HSs) compacted by interwoven nanoflakes.

The low ionic conductivity of solid-state electrolytes (SSEs) and the inferior interfacial reliability between SSEs and solid-state electrodes are two urgent challenges hindering the application of solid-state sodium batteries (SSSBs). Herein, sodium (Na) super ionic conductor (NASICON)-type SSEs with a nominal composition of Na3+2xZr2–xMgxSi2PO12 were synthesized using a facile two-step solid-state method, among which Na3.3Zr1.85Mg0.15Si2PO12 (x = 0.15, NZSP-Mg0.15) showed the highest ionic conductivity of 3.54 mS∙cm–1 at 25 °C. By means of a thorough investigation, it was verified that the composition of the grain boundary plays a crucial role in determining the total ionic conductivity of NASICON. Furthermore, due to a lack of examination in the literature regarding whether NASICON can provide enough anodic electrochemical stability to enable high-voltage SSSBs, we first adopted a high-voltage Na3(VOPO4)2F (NVOPF) cathode to verify its compatibility with the optimized NZSP-Mg0.15 SSE. By comparing the electrochemical performance of cells with different configurations (low-voltage cathode vs high-voltage cathode, liquid electrolytes vs SSEs), along with an X-ray photoelectron spectroscopy (XPS) evaluation of the after-cycled NZSP-Mg0.15, it was demonstrated that the NASICON SSEs are not stable enough under high voltage, suggesting the importance of investigating the interface between the NASICON SSEs and high-voltage cathodes. Furthermore, by coating NZSP-Mg0.15 NASICON powder onto a polyethylene (PE) separator (PE@NASICON), a 2.42 A∙h non-aqueous Na-ion cell of carbon|PE@NASICON|NaNi2/9Cu1/9Fe1/3Mn1/3O2 was found to deliver an excellent cycling performance with an 88% capacity retention after 2000 cycles, thereby demonstrating the high reliability of a separator coated with NASICON-type SSEs.

Manganese could be the element of choice for cathode materials used in large-scale energy storage systems owing to its abundance and low toxicity levels. However, both lithium- and sodium-ion batteries adopting this electrode chemistry suffer from rapid performance fading, suggesting a major technical barrier that must be overcome. Here we report a P3-type layered manganese oxide cathode Na0.6Li0.2Mn0.8O2 (NLMO) that delivers a high capacity of 240 mAh g−1 with outstanding cycling stability in a lithium half-cell. Combined experimental and theoretical characterizations reveal a characteristic topological feature that enables the good electrochemical performance. Specifically, the -α-γ- layer stack provides topological protection for lattice oxygen redox, whereas reversibility is absent in P2-structured NLMO, which takes an -α-β- configuration. The identified new order parameter opens an avenue towards the rational design of reversible Mn-rich cathode materials for sustainable batteries. Favoured cathodes for batteries should include abundant and redox-active elements, such as manganese. Here the authors report a Na0.6Li0.2Mn0.8O2 cathode design featuring a unique layer stacking sequence that provides topological protection to oxygen redox to overcome the performance fading.

Aqueous Li-ion batteries (ALIBs) are regarded as promising large-scale energy storage technology because of their intrinsic safety and cost-effectiveness. However, because of the “cathodic challenge” encountered using aqueous electrolytes, the choice of anode material is restricted to candidates having relatively high redox potential and low capacity, thus resulting in low energy density. In this communication, we report a TiO2 B anode for ALIBs that has low lithiation potential (∼1.6 V in nonaqueous electrolytes and ∼1.8 V in aqueous electrolytes), high capacity (∼200 mAh/g), and high structural stability. When the TiO2 B anode is paired with spinel LiMn2O4, the LiMn2O4//TiO2 B full cell can deliver high capacity (194.5 mAh/g, based on the anode mass) and high energy density (150 Wh/kg, based on the total electrode mass). Furthermore, a full cell employing this anode displays superior cycling performance with a high capacity retention of 76% after 400 cycles at 1 C, this is attributed to the structural stability of the TiO2 B nanowires and the wide electrochemical stability window of the Water-in-Salt (WIS) electrolyte. It is anticipated that the TiO2 B anode can provide a new option for constructing high-energy ALIBs.

Super-concentrated water-in-salt electrolytes make high-voltage aqueous batteries possible, but at the expense of high cost and several adverse effects, including high viscosity, low conductivity and slow kinetics. Here, we observe a concentration-dependent association between CO2 and TFSI anions in water that reaches maximum strength at 5 mol kg−1 LiTFSI. This TFSI–CO2 complex and its reduction chemistry allow us to decouple the interphasial responsibility of an aqueous electrolyte from its bulk properties, hence making high-voltage aqueous Li-ion batteries practical in dilute salt-in-water electrolytes. The CO2/salt-in-water electrolyte not only inherits the wide electrochemical stability window and non-flammability from water-in-salt electrolytes but also successfully circumvents the numerous disadvantages induced by excessive salt. This work represents a deviation from the water-in-salt pathway that not only benefits the development of practical aqueous batteries, but also highlights how the complex interactions between electrolyte components can be used to manipulate interphasial chemistry. Super-concentrated water-in-salt electrolytes enable high-voltage aqueous batteries, but have considerable drawbacks such as high viscosity, low conductivity and slow kinetics. Now a concentration-dependent association between CO2 and TFSI– has been discovered and leveraged to decouple the interphasial responsibility of an aqueous electrolyte from its bulk properties, making high-voltage aqueous Li-ion batteries practical in dilute salt-in-water electrolytes.

Inorganic solid-state electrolytes (ISSEs) are expected to achieve the application of lithium (Li) metal batteries. However, Li metal can still cause internal short circuit in solid electrolyte. Direct evidence is lacked to show how Li dendrites penetrate the solid electrolytes. Herein, an in-situ mini cell has been set up to study the behavior of Li growth inside garnet-type electrolyte. Transparent Li6.4La3Zr1.4Ta0.6O12 (LLZTO) pellets are prepared and employed in the in-situ optical observation. It is found that Li metal can deposit/dissolve inside LLZTO and a small amount of dead Li is left during dissolution step which may affect the subsequent deposition process. Besides, Li metal morphologies under different currents are characterized, which provides new insights into the mechanism of Li propagation in LLZTO. Finally, raising temperature is introduced to relieve Li dendrite effectively.

The operation of lithium-ion batteries involves electron removal from and filling into the redox orbitals of cathode materials, experimentally probing the orbital electron population thus is highly desirable to resolve the redox processes and charge compensation mechanism. Here, we combine quantitative convergent-beam electron diffraction with high-energy synchrotron powder X-ray diffraction to quantify the orbital populations of Co and O in the archetypal cathode material LiCoO2. The results indicate that removing Li ions from LiCoO2 decreases Co t2g orbital population, and the intensified covalency of Co–O bond upon delithiation enables charge transfer from O 2p orbital to Co eg orbital, leading to increased Co eg orbital population and oxygen oxidation. Theoretical calculations verify these experimental findings, which not only provide an intuitive picture of the redox reaction process in real space, but also offer a guidance for designing high-capacity electrodes by mediating the covalency of the TM–O interactions.

Na-based dual-ion batteries (DIBs) are a class of post-lithium technology with advantages including extremely fast charging, cost-effectiveness, and high natural abundance of raw materials. Operating up to high voltages (≈5.0 V), the decomposition of classic carbonate-based electrolyte formulations and the subsequent fade of capacity continues to be a major drawback in the development of these systems. Here, the performance of a Na-DIB was investigated in different commonly employed electrolyte system, and a highly concentrated (3 m NaPF

Na-ion batteries (NIBs) are gradually attracting much attention as an alternative to lead-acid batteries and supplement to Li-ion batteries (LIBs) owing to the abundant Na resources and excellent cost-effectiveness. Since the most commonly used graphite as an anode material in LIBs cannot be inherently used in NIBs, tremendous efforts have been made to advance the fundamental understanding and design of suitable anode materials for NIBs, including the improvement of Na storage capacity and the study on Na storage mechanisms. According to all these studies, disordered carbons are now the most promising anode candidates for NIBs. In this review, we discuss the current challenges and remaining problems to be solved in the area of disordered carbon anode materials for NIBs and provide future insights and research directions.

Na-ion batteries (NIBs) have been considered as potential candidates for large-scale energy storage, where O3-type Na-based layered oxide cathodes have attracted great attention due to their high capacity and low cost. However, O3-NaxTMO2 materials still suffer from insufficient air stability, which could lead to deteriorative electrochemical properties and thus hinder their practical application. In this work, a series of Al-doped O3-NaFe(1/3-x)Ni1/3Mn1/3AlxO2 cathodes prepared by a co-precipitation method were investigated to enhance their electrochemical performance and air stability through stabilizing their structural and interface chemical properties. The Al-doped O3-NaFe(1/3-0.01)Ni1/3Mn1/3Al0.01O2 (NFNMA0.01) cathode delivers a comparable capacity of 138 mAh g-1 and keeps a capacity retention of 85.88% after 50 cycles at 0.2 C, while the undoped O3-NaFe1/3Ni1/3Mn1/3O2 (NFNM) can only keep a capacity retention of 71.02%, although with an initial capacity of 141 mAh g-1 at 0.2 C. For the air stability, the capacity decay rates are 58.87 and 5.07% for the undoped NFNM and Al-doped NFNMA0.01 after the air exposure for 30 days, respectively. The greatly decaying electrochemical performance could be due to the formation of carbonates during air exposure, which can be efficiently suppressed by Al doping. The doped Al3+ has been confirmed to be inserted into the NFNM crystal lattice, inducing the reduced values of lattice parameters a and c due to the smaller ionic radius of Al3+ (53.5 pm) vs Fe3+ (55.0 pm). This study demonstrates that Al doping plays an important role in the air stability and cycling stability for layered cathode materials, which offers an efficient strategy to optimize the material design for their practical application in NIBs.

The lack of appropriate cathodes is restraining the advances of Mg batteries. Crystalline cathode materials suffer from sluggish reaction kinetics and low-capacity delivery. The finite type of crystalline structure further confines the rational design of cathode materials. Herein, we proposed amorphization and anion enrichment as a brand-new strategy to not only enhance the solid-state ion diffusion and provide more ion-storage sites in amorphous structure but also contribute to the local transfer of multiple electrons through the additional anionic redox centers. Accordingly, a series of amorphous titanium polysulfides (a-TiS x , x = 2, 3, and 4) were designed, which significantly outperformed their crystalline counterparts and achieved a highly competitive energy density of ∼260 Wh/kg. The unique Mg2+ storage mechanism involves the dissociation/formation of S-S bonds and changes in the coordination number of Ti, namely, a mixture of conversion and intercalation reaction, accompanied by the joint cationic (Ti) and anionic (S) redox-rich chemistry. Our proposed amorphous and redox-rich design philosophy might provide an innovative direction for developing high-performance cathode materials for multivalent-ion batteries.

Na-based batteries have shown substantial progress in recent years and are promising candidates for mitigating the supply risks associated with Li-based batteries. In this Review, Na and Li batteries are compared in terms of fundamental principles and specific materials. Principles for the rational design of a Na battery architecture are discussed. Recent prototypes are surveyed to demonstrate that Na cells offer realistic alternatives that are competitive with some Li cells in terms of performance. Sodium batteries are promising candidates for mitigating the supply risks associated with lithium batteries. This Review compares the two technologies in terms of fundamental principles and specific materials, and assesses the performance of commercial prototype sodium cells.

The growing concern about scarcity and large-scale applications of lithium resources has attracted efforts to realize cost-effective phosphate-based cathode materials for next-generation Na-ion batteries (NIBs). In previous work, a series of materials (such as Na4Fe3(PO4)2(P2O7), Na3VCr(PO4)3, Na4VMn(PO4)3, Na3MnTi(PO4)3, Na3MnZr(PO4)3, etc) with ∼120 mAh g−1 specific capacity and high operating potential has been proposed. However, the mass ratio of the total transition metal in the above compounds is only ∼22 wt%, which means that one-electron transfer for each transition metal shows a limited capacity (the mass ratio of Fe is 35.4 wt% in LiFePO4). Therefore, a multi-electron transfer reaction is necessary to catch up to or go beyond the electrochemical performance of LiFePO4. This review summarizes the reported NASICON-type and other phosphate-based cathode materials. On the basis of the aforementioned experimental results, we pinpoint the multi-electron behavior of transition metals and shed light on designing rules for developing high-capacity cathodes in NIBs.

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 ).

Poly(ethylene oxide)-based solid-state electrolytes are widely considered promising candidates for the next generation of lithium and sodium metal batteries. However, several challenges, including low oxidation resistance and low cation transference number, hinder poly(ethylene oxide)-based electrolytes for broad applications. To circumvent these issues, here, we propose the design, synthesis and application of a fluoropolymer, i.e., poly(2,2,2-trifluoroethyl methacrylate). This polymer, when introduced into a poly(ethylene oxide)-based solid electrolyte, improves the electrochemical window stability and transference number. Via multiple physicochemical and theoretical characterizations, we identify the presence of tailored supramolecular bonds and peculiar morphological structures as the main factors responsible for the improved electrochemical performances. The polymeric solid electrolyte is also investigated in full lithium and sodium metal lab-scale cells. Interestingly, when tested in a single-layer pouch cell configuration in combination with a Li metal negative electrode and a LiMn0.6Fe0.4PO4-based positive electrode, the polymeric solid-state electrolyte enables 200 cycles at 42 mA·g−1 and 70 °C with a stable discharge capacity of approximately 2.5 mAh when an external pressure of 0.28 MPa is applied.

Sodium metal batteries are attracting increasing attention on account of their high energy densities as well as the abundance of sodium-based resources. However, the uneven metallic deposition and dendrite formation during cycling hinder the application of sodium metal anodes. Carbon skeletons have been reported in the literature to mitigate the dendrite formation during the plating and stripping of metallic sodium. Still, the role played by different carbon structural features (i.e., pores vs. defects) and relative mechanisms are not well understood, preventing the controllable interface engineering at the anode side. Here, we have rationally designed the structural features of sustainable carbon skeletons from a renewable precursor to unveil the roles of defects and pores for metallic deposition. The obtained carbon skeleton with rich defects and negligible pores exhibits the best performance when applied to protect metal anodes. After long cycling (>1200 hours), the retained high Coulombic efficiency (∼99.9%) of the plating and stripping processes indicates the importance of defects for inducing uniform metallic deposition. Combined with different types of cathodes (e.g., Prussian blue and sulfur), “anode-less” sodium metal batteries with enhanced electrochemical performance are also demonstrated in terms of sustainability.

The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal (TM) oxide studies in various fields, especially on the fervent topic of oxygen redox states in battery electrodes. However, critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions, which has been a popular practice in the battery field. This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements, structures and electrochemical states through combined experimental and theoretical analyses. It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states. Furthermore, the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window, leading to a summary map of the relative energy positions of the low-lying TM states, with higher TM oxidation states at lower energies, corresponding to higher electrochemical potentials. The results naturally clarify some unusual redox reactions, such as Cr3+/6+. This work provides a critical clarification on O-K pre-edge interpretation and more importantly, a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.