Creep-type all-solid-state cathode achieving long life.

Electrochemical-mechanical coupling poses enormous challenges to the interfacial and structural stability but create new opportunities to design innovative all-solid-state batteries from scratch. Relying on the solid-solid constraint in the space-limited domain structure, we propose to exploit the lithiation-induced stress to drive the active materials creep, thereby improving the structural integrity. For demonstration, we fabricate the creep-type all-solid-state cathode using creepable Se material and an all-in-one rigid ionic/electronic conducting Mo6Se8 framework. As indicated by the in-situ experiment and numerical simulation, this cathode presents unique capabilities in improving interparticle contact and avoiding particle fracture, leading to its superior electrochemical performance, including a superior long-cycle life of more than 3000 cycles at 0.5 C and a high volumetric energy density of 2460 Wh/L at the cathode level. We believe this innovative strategy to utilize mechanics to boost the electrochemical performance could shed light on the future design of all-solid-state batteries for practical applications.

Aluminum corrosion-passivation regulation prolongs aqueous batteries life.

Aluminum current collectors are widely used in nonaqueous batteries owing to their cost-effectiveness, lightweightness, and ease of fabrication. However, they are excluded from aqueous batteries due to their severe corrosion in aqueous solutions. Here, we propose hydrolyzation-type anodic additives to form a robust passivation layer to suppress corrosion. These additives dramatically lower the corrosion current density of aluminum by nearly three orders of magnitude to ~10-6 A cm-2. In addition, realizing that electrochemical corrosion accompanies anode prelithiation, we propose a prototype of self-prolonging aqueous Li-ion batteries (Al ||LiMn2O4 ||TiO2), whose capacity retention rises from 49.5% to 70.1% after 200 cycles. A sacrificial aluminum electrode where electrochemical corrosion is utilized is introduced as an electron supplement to prolong the cycling life of aqueous batteries. Our work addresses the short-life issue of aqueous batteries resulting from the corrosion of the current collector and lithium loss from side reactions.

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.

Electrolyte design combining fluoro- with cyano-substitution solvents for anode-free Li metal batteries.

Fluoro-substitution solvents have achieved great success in electrolyte engineering for high-energy lithium metal batteries, which, however, is beset by low solvating power, thermal and chemical instability, and possible battery swelling. Instead, we herein introduce cyanogen as the electron-withdrawing group to enhance the oxidative stability of ether solvents, in which cyanogen and ether oxygen form the chelating structure with Li+ not notably undermining the solvating power. Cyano-group strongly bonds with transition metals (TMs) of NCM811 cathode to attenuate the catalytic reactivity of TMs toward bulk electrolytes. Besides, a stable and uniform cathode-electrolyte interphase (CEI) inhibits the violent oxidation decomposition of electrolytes and guarantees the structural integrity of the NCM811 cathode. Also, a N-containing and LiF-rich solid-electrolyte interphase (SEI) in our electrolyte facilitates fast Li+ migration and dense Li deposition. Accordingly, our electrolyte enables a stable cycle of Li metal anode with Coulombic efficiency of 98.4% within 100 cycles. 81.8% capacity of 4.3 V NCM811 cathode remains after 200 cycles. Anode-free pouch cells with a capacity of 125 mAh maintain 76% capacity after 100 cycles, corresponding to an energy density of 397.5 Wh kg-1.

Highly Efficient Spatially-Temporally Synchronized Construction of Robust Li3 PO4 -rich Solid-Electrolyte Interphases in Aqueous Li-ion Batteries.

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 Li3 PO4 -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 (H2 PO4 - ) shift to insoluble solid Li3 PO4 . It is worth highlighting that the Li3 PO4 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.

The evolution of anionic nanoclusters at the electrode interface in water-in-salt electrolytes.

Water-in-salt electrolytes (WiSEs) have attracted extensive attention as promising alternatives to organic electrolytes. The limited electrochemical stability windows (ESWs) of aqueous electrolytes are significantly widened by WiSEs. However, the actual ESWs are lower than predicted as the interphase with WiSEs is not as stable as the solid electrolyte interphase (SEI) in conventional lithium-ion batteries. Therefore, identifying the interface state in WiSEs is vital to understanding their electrochemical behavior. Here, the structure of the lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) electrolyte near the interface of the carbon electrode (Ketjen black) was evaluated by experimental methods (neutron diffraction, Raman, and nuclear magnetic resonance spectroscopy) and molecular dynamics (MD) simulations. The results reveal that the introduction of carbon electrodes increases the size of the anionic nanoclusters and enhances the microphase separation at the interface. The MD simulations show that cation-π interactions are responsible for the evolution of anionic nanoclusters at the electrode interface. Moreover, lower charge transfer resistance is achieved at carbon-based electrodes due to the specific interface state. Our findings provide a strategy for introducing cation-π interactions between electrodes and electrolytes to improve the electrochemical performance.

The Proof-of-Concept of Anode-Free Rechargeable Mg Batteries.

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 Mg2 Mo6 S8 -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 Mg2 Mo6 S8 and MgS acts as the active material to reversibly provide high capacities. Besides, Mg2 Mo6 S8 shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode-free Mg2 Mo6 S8 -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.

Anion-enrichment interface enables high-voltage anode-free lithium metal 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.

A New Zinc Salt Chemistry for Aqueous Zinc-Metal Batteries.

Aqueous zinc-ion batteries (ZIBs) are promising energy storage solutions with low cost and superior safety, but they suffer from chemical and electrochemical degradations closely related to the electrolyte. Here, a new zinc salt design and a drop-in solution for long cycle-life aqueous ZIBs are reported. The salt Zn(BBI)2 with a rationally designed anion group, N-(benzenesulfonyl)benzenesulfonamide (BBI- ), has a special amphiphilic molecular structure, which combines the benefits of hydrophilic and hydrophobic groups to properly tune the solubility and interfacial condition. This new zinc salt does not contain fluorine and is synthesized via a high-yield and low-cost method. It is shown that 1 m Zn(BBI)2 aqueous electrolyte with a widened cathodic stability window effectively stabilizes Zn metal/H2 O interface, mitigates chemical and electrochemical degradations, and enables both symmetric and full cells using a zinc-metal electrode.

An Electric-Field-Reinforced Hydrophobic Cationic Sieve Lowers the Concentration Threshold of Water-In-Salt Electrolytes.

High-concentration water-in-salt (WIS) electrolytes expand the stable electrochemical window of aqueous electrolytes, leading to the advent of high-voltage (above 2 V) aqueous Li-ion batteries (ALIBs). However, the high lithium salt concentration electrolytes of ALIBs result in their high cost and deteriorate kinetic performance. Therefore, it is challenging for ALIBs to explore aqueous electrolytes with appropriate concentration to balance the electrochemical window and kinetic performance as well as the cost. In contrast to maintaining high concentrations of aqueous electrolytes (>20 m), a small number of hydrophobic cations are introduced to a much lower electrolyte concentration (13.8 m), and it is found that, compared with WIS electrolytes, ALIBs with these concentration-lowered electrolytes possess a compatible stable electrochemical window (3.23 V) and achieve better kinetic performance. These findings originate from the added cations, which form an electric-field-reinforced hydrophobic cationic sieve (HCS) that blocks water away from the anode and suppresses the hydrogen evolution reaction. Meanwhile, the lower electrolyte concentration provides significant benefits to ALIBs, including lower cost, better rate capability (lower viscosity of 18 cP and higher ionic conductivity of 22 mS cm-1 at 25 °C), and improved low-temperature performance (liquidus temperature of -10.18 °C).

Rational design of a topological polymeric solid electrolyte for high-performance all-solid-state alkali metal batteries.

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.

A Better Choice to Achieve High Volumetric Energy Density: Anode-Free Lithium-Metal Batteries.

Volumetric energy density is a critical but easily neglected index of lithium-metal batteries (LMBs). Compared with gravimetric energy density, the volumetric energy density (VED) of LMBs is much more sensitive to the anode/cathode (A/C) ratio due to the low density of lithium (Li) metal and the volume expansion of the Li-metal anode owing to its pulverization during cycles. Anode-free LMBs (AF-LMBs) have high theoretical VED due to the absence of an anode and high retention with relatively low cell expansion. Because Li plating highly depends on the mother substrate, Li plating on copper (Cu) substrates is more reversible and denser than that on Li substrates during cycling, which is beneficial for maintaining high volumetric capacity and efficient Li utilization. Therefore, considering that excess Li must be strictly limited to achieve competitive energy density, AF-LMBs (with bare Cu foil as the anode current collector) for high-volumetric-density batteries are recommended.

Aqueous interphase formed by CO2 brings electrolytes back to salt-in-water regime.

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.

Amorphous Redox-Rich Polysulfides for Mg Cathodes.

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.

Low-Density Fluorinated Silane Solvent Enhancing Deep Cycle Lithium-Sulfur Batteries' Lifetime.

The lithium metal anode (LMA) instability at deep cycle with high utilization is a crucial barrier for developing lithium (Li) metal batteries, resulting in excessive Li inventory and electrolyte demand. This issue becomes more severe in capacity-type lithium-sulfur (Li-S) batteries. High-concentration or localized high-concentration electrolytes are noted as effective strategies to stabilize Li metal but usually lead to a high electrolyte density (>1.4 g mL-1 ). Here we propose a bifunctional fluorinated silane-based electrolyte with a low density of 1.0 g mL-1 that not only is much lighter than conventional electrolytes (≈1.2 g mL-1 ) but also form a robust solid electrolyte interface to minimize Li depletion. Therefore, the Li loss rate is reduced over 4.5-fold with the proposed electrolyte relative to its conventional counterpart. When paired with onefold excess LMA at the electrolyte weight/cell capacity (E/C) ratio of 4.5 g Ah-1 , the Li-S pouch cell using our electrolyte can survive for 103 cycles, much longer than with the conventional electrolyte (38 cycles). This demonstrates that our electrolyte not only reduces the E/C ratio but also enhances the cyclic stability of Li-S batteries under limited Li amounts.

Amorphous anion-rich titanium polysulfides for aluminum-ion batteries.

The strong electrostatic interaction between Al3+ and close-packed crystalline structures, and the single-electron transfer ability of traditional cationic redox cathodes, pose challenged for the development of high-performance rechargeable aluminum batteries. Here, to break the confinement of fixed lattice spacing on the diffusion and storage of Al-ion, we developed a previously unexplored family of amorphous anion-rich titanium polysulfides (a-TiS x , x = 2, 3, and 4) (AATPs) with a high concentration of defects and a large number of anionic redox centers. The AATP cathodes, especially a-TiS4, achieved a high reversible capacity of 206 mAh/g with a long duration of 1000 cycles. Further, the spectroscopy and molecular dynamics simulations revealed that sulfur anions in the AATP cathodes act as the main redox centers to reach local electroneutrality. Simultaneously, titanium cations serve as the supporting frameworks, undergoing the evolution of coordination numbers in the local structure.

Dense All-Electrochem-Active Electrodes for All-Solid-State Lithium Batteries.

The energy density presents the core competitiveness of lithium (Li)-ion batteries. In conventional Li-ion batteries, the utilization of the gravimetric/volumetric energy density at the electrode level is unsatisfactory (<84 wt% and <62 vol%, respectively) due to the existence of non-electrochemical active parts among the 3D porous electrodes, including electrolytes, binders, and carbon additives. These are regarded as indispensable and irreducible components of the electronic and ionic transport network. Here, a dense "all-electrochem-active" (AEA) electrode for all-solid-state Li batteries is proposed, which is entirely constructed from a family of superior mixed electronic-ionic-conducting cathodes, to minimize the energy density gap between the accessible and theoretical energy density at the electrode level. Furthermore, with the ionic-electronic-conductive network self-supported from the AEA cathode, the dense hybrid sulfur (S)-based AEA electrode exhibits a high compacted filling rate of 91.8%, which indicates a high energy density of 777 W h kg-1 and 1945 W h L-1 at the electrode level based on the total cathodes and anodes when at 70 °C.

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.

Electronic Conductive Inorganic Cathodes Promising High-Energy Organic Batteries.

The electrochemical utilization of organic electrode materials (OEMs) is highly dependent on an excess amount of inactive carbon at the expense of low packing density and energy density. In this work, the challenges by substituting inactive carbon with electronic conductive inorganic cathode (ECIC) materials, which are endowed with high electronic conductivity to transport electrons for redox reactions of the whole electrodes, high ion-storage capacity to act as secondary active materials, and strong affinity with OEMs to inhibit their dissolution, are addressed. Combining representative ECICs (TiS2 and Mo6 S8 ) with organic electrode materials (perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and hexaazatrinaphthalene (HATN)) simultaneously achieves high capacity, low porosity, lean electrolyte, and thus high energy density. High gravimetric and volumetric energy densities of 153 Wh kg-1 and 200 Wh L-1 are delivered with superior cycling stability in a 30 mA h-level Li/PTCDA-TiS2 pouch cell. The proof-of-concept of organic-ECIC electrodes is also successfully demonstrated in monovalent Na, divalent Mg, and trivalent Al batteries, indicating their feasibility and generalizability. With the discovery of more ECIC materials and OEMs, it is anticipated that the proposed organic-ECIC system can result in further improvements at cell level to compete with transition metal-based Li-ion 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 ).