Tailored Organic Electrode Material Compatible with Sulfide Electrolyte for Stable All‐Solid‐State Sodium Batteries

All‐solid‐state sodium batteries (ASSSBs) with nonflammable electrolytes and ubiquitous sodium resource are a promising solution to the safety and cost concerns for lithium‐ion batteries. However, the intrinsic mismatch between low anodic decomposition potential of superionic sulfide electrolytes and high operating potentials of sodium‐ion cathodes leads to a volatile cathode–electrolyte interface and undesirable cell performance. Here we report a high‐capacity organic cathode, Na₄C₆O₆, that is chemically and electrochemically compatible with sulfide electrolytes. A bulk‐type ASSSB shows high specific capacity (184 mAh g^?1) and one of the highest specific energies (395 Wh kg^?1) among intercalation compound‐based ASSSBs. The capacity retentions of 76 % after 100 cycles at 0.1 C and 70 % after 400 cycles at 0.2 C represent the record stability for ASSSBs. Additionally, Na₄C₆O₆ functions as a capable anode material, enabling a symmetric all‐organic ASSSB with Na₄C₆O₆ as both cathode and anode materials.     

Design of Advanced MnO/N‐Gr 3D Walls through Polymer Cross‐Linking for High‐Performance Supercapacitor

Three‐dimensional, vertically aligned MnO/nitrogen‐doped graphene (3D MnO/N‐Gr) walls were prepared through facile solution‐phase synthesis followed by thermal treatment. Polyvinylpyrrolidone (PVP) was strategically added to generate cross‐links to simultaneously form 3D wall structures and to incorporate nitrogen atoms into the graphene network. The unique wall features of the as‐prepared 3D MnO/N‐Gr hybirdes provide a large surface area (91.516 m² g^?1) and allow for rapid diffusion of the ion electrolyte, resulting in a high specific capacitance of 378 F g^?1 at 0.25 A g^?1 and an excellent charge/discharge stability (93.7 % capacity retention after 8000 cycles) in aqueous 1 m Na₂SO₄ solution as electrolyte. Moreover, the symmetric supercapacitors that were rationally designed by using 3D MnO/N‐Gr hybrids exhibit outstanding electrochemical performance in an organic electrolyte with an energy density of 90.6 Wh kg^?1 and a power density of 437.5 W kg^?1.     

Synergistic Dual‐Additive Electrolyte Enables Practical Lithium‐Metal Batteries

A rechargeable Li metal anode coupled with a high‐voltage cathode is a promising approach to high‐energy‐density batteries exceeding 300 Wh kg^?1. Reported here is an advanced dual‐additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate‐based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F‐ and B‐containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg^?1 at cell‐level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.     

Rechargeable Room‐Temperature Na–CO2 Batteries

Developing rechargeable Na–CO₂ batteries is significant for energy conversion and utilization of CO₂. However, the reported batteries in pure CO₂ atmosphere are non‐rechargeable with limited discharge capacity of 200 mAh g^?1. Herein, we realized the rechargeability of a Na–CO₂ battery, with the proposed and demonstrated reversible reaction of 3 CO₂+4 Na?2 Na₂CO₃+C. The battery consists of a Na anode, an ether‐based electrolyte, and a designed cathode with electrolyte‐treated multi‐wall carbon nanotubes, and shows reversible capacity of 60000 mAh g^?1 at 1 A g^?1 (≈1000 Wh kg^?1) and runs for 200 cycles with controlled capacity of 2000 mAh g^?1 at charge voltage <3.7 V. The porous structure, high electro‐conductivity, and good wettability of electrolyte to cathode lead to reduced electrochemical polarization of the battery and further result in high performance. Our work provides an alternative approach towards clean recycling and utilization of CO₂.     

Concentrated Electrolyte for the Sodium–Oxygen Battery: Solvation Structure and Improved Cycle Life

Alkali metal–oxygen batteries are of great interests for energy storage because of their unparalleled theoretical energy densities. Particularly attractive is the emerging Na–O₂ battery because of the formation of superoxide as the discharge product. Dimethyl sulfoxide (DMSO) is a promising solvent for this battery but its instability towards Na makes it impractical in the Na–O₂ battery. Herein we report the enhanced stability of Na in DMSO solutions containing concentrated sodium trifluoromethanesulfonimide (NaTFSI) salts (>3 mol kg^?1). Raman spectra of NaTFSI/DMSO electrolytes and ab initio molecular dynamics simulation reveal the Na⁺ solvation number in DMSO and the formation of Na(DMSO)₃(TFSI)‐like solvation structure. The majority of DMSO molecules solvating Na⁺ in concentrated solutions reduces the available free DMSO molecules that can react with Na and renders the TFSI anion decomposition, which protects Na from reacting with the electrolyte. Using these concentrated electrolytes, Na–O₂ batteries can be cycled forming sodium superoxide (NaO₂) as the sole discharge product with improved long cycle life, highlighting the beneficial role of concentrated electrolytes for Na‐based batteries.     

Superoxide Stabilization and a Universal KO2 Growth Mechanism in Potassium–Oxygen Batteries

Rechargeable potassium–oxygen (K‐O₂) batteries promise to provide higher round‐trip efficiency and cycle life than other alkali–oxygen batteries with satisfactory gravimetric energy density (935 Wh kg^?1). Exploiting a strong electron‐donating solvent, for example, dimethyl sulfoxide (DMSO) strongly stabilizes the discharge product (KO₂), resulting in significant improvement in electrode kinetics and chemical/electrochemical reversibility. The first DMSO‐based K‐O₂ battery demonstrates a much higher energy efficiency and stability than the glyme‐based electrolyte. A universal KO₂ growth model is developed and it is demonstrated that the ideal solvent for K‐O₂ batteries should strongly stabilize superoxide (strong donor ability) to obtain high electrode kinetics and reversibility while providing fast oxygen diffusion to achieve high discharge capacity. This work elucidates key electrolyte properties that control the efficiency and reversibility of K‐O₂ batteries.     

A Porous Network of Bismuth Used as the Anode Material for High‐Energy‐Density Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are plagued by a lack of materials for reversible accommodation of the large‐sized K⁺ ion. Herein we present, the Bi anode in combination with the dimethoxyethane‐(DME) based electrolyte to deliver a remarkable capacity of ca. 400 mAh g^?1 and long cycle stability with three distinct two‐phase reactions of Bi? KBi₂?K₃Bi₂?K₃Bi. These are ascribed to the gradually developed three‐dimensional (3D) porous networks of Bi, which realizes fast kinetics and tolerance of its volume change during potassiation and depotassiation. The porosity is linked to the unprecedented movement of the surface Bi atoms interacting with DME molecules, as suggested by DFT calculations. A full KIB of Bi//DME‐based electrolyte//Prussian blue of K_0.72Fe[Fe(CN)₆] is demonstrated to present large energy density of 108.1 Wh kg^?1 with average discharge voltage of 2.8 V and capacity retention of 86.5 % after 350 cycles.     

Lithium‐Rich Layered Oxide Li1.18Ni0.15Co0.15Mn0.52O2 as the Cathode Material for Hybrid Sodium‐Ion Batteries

Li‐rich layered oxide Li_1.18Ni_0.15Co_0.15Mn_0.52O₂ (LNCM) is, for the first time, examined as the positive electrode for hybrid sodium‐ion battery and its Na⁺ storage properties are comprehensively studied in terms of galvanostatic charge–discharge curves, cyclic voltammetry and rate capability. LNCM in the proposed sodium‐ion battery demonstrates good rate capability whose discharge capacity reaches about 90 mA h g^?1 at 10 C rate and excellent cycle stability with specific capacity of about 105 mA h g^?1 for 200 cycles at 5 C rate. Moreover, ex situ ICP‐OES suggests interesting mixed‐ions migration processes: In the initial two cycles, only Li⁺ can intercalate into the LNCM cathode, whereas both Li⁺ and Na⁺ work together as the electrochemical cycles increase. Also the structural evolution of LNCM is examined in terms of ex situ XRD pattern at the end of various charge–discharge scans. The strong insight obtained from this study could be beneficial to the design of new layered cathode materials for future rechargeable sodium‐ion batteries.     

All Organic Sodium‐Ion Batteries with Na4C8H2O6

Developing organic compounds with multifunctional groups to be used as electrode materials for rechargeable sodium‐ion batteries is very important. The organic tetrasodium salt of 2,5‐dihydroxyterephthalic acid (Na₄DHTPA; Na₄C₈H₂O₆), which was prepared through a green one‐pot method, was investigated at potential windows of 1.6–2.8 V as the positive electrode or 0.1–1.8 V as the negative electrode (vs. Na⁺/Na), each delivering compatible and stable capacities of ca. 180 mAh g^?1 with excellent cycling. A combination of electrochemical, spectroscopic and computational studies revealed that reversible uptake/removal of two Na⁺ ions is associated with the enolate groups at 1.6–2.8 V (Na₂C₈H₂O₆/Na₄C₈H₂O₆) and the carboxylate groups at 0.1–1.8 V (Na₄C₈H₂O₆/Na₆C₈H₂O₆). The use of Na₄C₈H₂O₆ as the initial active materials for both electrodes provided the first example of all‐organic rocking‐chair SIBs with an average operation voltage of 1.8 V and a practical energy density of about 65 Wh kg^?1.     

Electrochemically Generated γ‐LixV2O5 as Insertion Host for High‐Energy Li‐Ion Capacitors

In this study, we explored the feasibility of using electrochemically generated γ‐Li_xV₂O₅ as an insertion‐type anode in the lithium‐ion capacitor (LIC) with activated carbon (AC) as a cathode. Along with the native form of V₂O₅, their carbon composites are also used as the electrode material which is prepared by high‐energy ball milling. The electrochemical pre‐lithiation strategy is used to generate the desired γ‐phase of V₂O₅ (γ‐Li_xV₂O₅). Under the optimized mass loading conditions, the LICs are assembled with γ‐Li_xV₂O₅ as anode and AC as a cathode in the organic medium. Among the different LICs fabricated, AC/γ‐Li_xV₂O₅‐BM50 configuration delivered an energy density of 33.91 Wh kg^?1 @ 0.22 kW kg^?1 with excellent capacity retention characteristics. However, a dramatic increase in energy density (43.98 Wh kg^?1@0.28 kW kg^?1) is noted after the electrolyte modification with fluoroethylene carbonate. The high temperature performance of the assembled LIC is also studied and found that γ‐Li_xV₂O₅ phase can be used as a potential battery‐type component to construct high‐performance hybrid charge storage devices.     

Synergy of Epoxy Chemical Tethers and Defect‐Free Graphene in Enabling Stable Lithium Cycling of Silicon Nanoparticles

We report a new approach for nanosilicon–graphene hybrids with uniquely stable solid electrolyte interphase. Expanded graphite is gently exfoliated creating “defect‐free” graphene that is non‐catalytic towards electrolyte decomposition, simultaneously introducing high mass loading (48 wt. %) Si nanoparticles. Silane surface treatment creates epoxy chemical tethers, mechanically binding nano‐Si to CMC binder through epoxy ring‐opening reaction while stabilizing the Si surface chemistry. Epoxy‐tethered silicon pristine–graphene hybrid “E‐Si‐pG” exhibits state‐of‐the‐art performance in full battery opposing commercial mass loading (12 mg cm^?2) LiCoO₂ (LCO) cathode. At 0.4 C, with areal capacity of 1.62 mAh cm^?2 and energy of 437 Wh kg^?1, achieving 1.32 mAh cm^?2, 340.4 Wh kg^?1 at 1 C. After 150 cycles, it retains 1.25 mAh cm^?2, 306.5 Wh kg^?1. Sputter‐down XPS demonstrates survival of surface C‐Si‐O‐Si groups in E‐Si‐pG after repeated cycling. The discovered synergy between support defects, chemical‐mechanical stabilization of Si surfaces, and SEI‐related failure may become key LIB anode design rule.     

Experimental and Computational Analysis of the Solvent‐Dependent O2/Li+‐O2− Redox Couple: Standard Potentials,Coupling Strength,and Implications for Lithium–Oxygen Batteries

Understanding and controlling the kinetics of O₂ reduction in the presence of Li⁺‐containing aprotic solvents, to either Li⁺‐O₂^? by one‐electron reduction or Li₂O₂ by two‐electron reduction, is instrumental to enhance the discharge voltage and capacity of aprotic Li‐O₂ batteries. Standard potentials of O₂/Li⁺‐O₂^? and O₂/O₂^? were experimentally measured and computed using a mixed cluster‐continuum model of ion solvation. Increasing combined solvation of Li⁺ and O₂^? was found to lower the coupling of Li⁺‐O₂^? and the difference between O₂/Li⁺‐O₂^? and O₂/O₂^? potentials. The solvation energy of Li⁺ trended with donor number (DN), and varied greater than that of O₂^? ions, which correlated with acceptor number (AN), explaining a previously reported correlation between Li⁺‐O₂^? solubility and DN. These results highlight the importance of the interplay between ion–solvent and ion–ion interactions for manipulating the energetics of intermediate species produced in aprotic metal–oxygen batteries.     

A Sustainable Solid Electrolyte Interphase for High‐Energy‐Density Lithium Metal Batteries Under Practical Conditions

High‐energy‐density Li metal batteries suffer from a short lifespan under practical conditions, such as limited lithium, high loading cathode, and lean electrolytes, owing to the absence of appropriate solid electrolyte interphase (SEI). Herein, a sustainable SEI was designed rationally by combining fluorinated co‐solvents with sustained‐release additives for practical challenges. The intrinsic uniformity of SEI and the constant supplements of building blocks of SEI jointly afford to sustainable SEI. Specific spatial distributions and abundant heterogeneous grain boundaries of LiF, LiN_xO_y, and Li₂O effectively regulate uniformity of Li deposition. In a Li metal battery with an ultrathin Li anode (33 μm), a high‐loading LiNi_0.5Co_0.2Mn_0.3O₂ cathode (4.4 mAh cm^?2), and lean electrolytes (6.1 g Ah^?1), 83 % of initial capacity retains after 150 cycles. A pouch cell (3.5 Ah) demonstrated a specific energy of 340 Wh kg^?1 for 60 cycles with lean electrolytes (2.3 g Ah^?1).     

Realizing Complete Solid‐Solution Reaction in High Sodium Content P2‐Type Cathode for High‐Performance Sodium‐Ion Batteries

P2‐type layered oxides suffer from an ordered Na⁺/vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na⁺ extraction/insertion. The deficient sodium in the P2‐type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na⁺ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2‐type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau‐free P2‐type cathode‐Na_0.85Li_0.12Ni_0.22Mn_0.66O₂ (P2‐NLNMO) was developed. The complete solid‐solution reaction over a wide voltage range ensures both fast Na⁺ mobility (10^?11 to 10^?10 cm² s^?1) and small volume variation (1.7 %). The high sodium content P2‐NLNMO exhibits a higher reversible capacity of 123.4 mA h g^?1, superior rate capability of 79.3 mA h g^?1 at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid‐solution reaction are critical to realizing high‐performance P2‐type cathodes for sodium‐ion batteries.     

Na2S–Carbon Nanotube Fabric Electrodes for Room‐Temperature Sodium–Sulfur Batteries

A unique sodium sulfide (Na₂S) cathode is developed, which will allow the use of sodium‐free anodes for room‐temperature sodium–sulfur (Na–S) batteries. To overcome the “inert” nature of the Na₂S, a special cathode structure is developed by spreading the multi‐walled carbon nanotube (MWCNT)‐wrapped Na₂S particles onto MWCNT fabrics. Spectroscopic and electrochemical analyses reveal a series of polysulfide intermediates involved in the charge/discharge of the cell. The Na–S battery prepared in full discharge state with the Na₂S/MWCNT cathode provides a remarkable capacity of 500 A h kg^?1 (based on sulfur mass) after 50 cycles.     

Electrochemical and Structural Study of Layered P2‐Type Na2/3Ni1/3Mn2/3O2 as Cathode Material for Sodium‐Ion Battery

P2‐type Na_2/3Ni_1/3Mn_2/3O₂ was synthesized by a controlled co‐precipitation method followed by a high‐temperature solid‐state reaction and was used as a cathode material for a sodium‐ion battery (SIB). The electrochemical behavior of this layered material was studied and an initial discharge capacity of 151.8 mA h g^?1 was achieved in the voltage range of 1.5–3.75 V versus Na⁺/Na. The retained discharge capacity was found to be 123.5 mA h g^?1 after charging/discharging 50 cycles, approximately 81.4 % of the initial discharge capacity. In situ X‐ray diffraction analysis was used to investigate the sodium insertion and extraction mechanism and clearly revealed the reversible structural changes of the P2‐Na_2/3Ni_1/3Mn_2/3O₂ and no emergence of the O2‐Ni_1/3Mn_2/3O₂ phase during the cycling test, which is important for designing stable and high‐performance SIB cathode materials.     

Advanced High‐Voltage Aqueous Lithium‐Ion Battery Enabled by “Water‐in‐Bisalt” Electrolyte

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.     

Sodium‐Doped Mesoporous Ni2P2O7 Hexagonal Tablets for High‐Performance Flexible All‐Solid‐State Hybrid Supercapacitors

A simple hydrothermal method has been developed to prepare hexagonal tablet precursors, which are then transformed into porous sodium‐doped Ni₂P₂O₇ hexagonal tablets by a simple calcination method. The obtained samples were evaluated as electrode materials for supercapacitors. Electrochemical measurements show that the electrode based on the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets exhibits a specific capacitance of 557.7 F g^?1 at a current density of 1.2 A g^?1. Furthermore, the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets were successfully used to construct flexible solid‐state hybrid supercapacitors. The device is highly flexible and achieves a maximum energy density of 23.4 Wh kg^?1 and a good cycling stability after 5000 cycles, which confirms that the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets are promising active materials for flexible supercapacitors.     

Formation of Superoxo Species by Interaction of O2 with Na Atoms Deposited on MgO Powders: A Combined Continuous‐Wave EPR (CW‐EPR), Hyperfine Sublevel Correlation (HYSCORE) and DFT Study

The formation of O₂^? radical anions by contact of O₂ molecules with a Na pre‐covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O₂. The typical EPR signal of isolated Na atoms disappears when the reaction with O₂ takes place and new paramagnetic species are observed, which are attributed to different surface‐stabilised O₂^? radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O₂^?Na⁺ species to be determined, demonstrating the direct coordination of the O₂^? adsorbate to surface Na⁺ cations. DFT calculations enable the structural details of the formed species to be determined. Matrix‐isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface‐stabilised Na⁺? O₂^? complexes.     

A High‐Voltage and Ultralong‐Life Sodium Full Cell for Stationary Energy Storage

Recently, there has been great interest in developing advanced sodium‐ion batteries for large‐scale application. Most efforts have concentrated on the search for high‐performance electrode materials only in sodium half‐cells. Research on sodium full cells for practical application has encountered many problems, such as insufficient cycles with rapid capacity decay, low safety, and low operating voltage. Herein, we present a layered P2‐Na_0.66Ni_0.17Co_0.17Ti_0.66O₂, as both an anode (ca. 0.69 V versus Na⁺/Na) and as a high‐voltage cathode (ca. 3.74 V versus Na⁺/Na). The full cell based on this bipolar electrode exhibits well‐defined voltage plateaus near 3.10 V, which is the highest average voltage in the symmetric cells. It also shows the longest cycle life (75.9 % capacity retention after 1000 cycles) in all sodium full cells, a usable capacity of 92 mAh g^?1, and superior rate capability (65 mAh g^?1 at a high rate of 2C).