A green and sustainable strategy toward lithium resources recycling from spent batteries.

Recycling lithium from spent batteries is challenging because of problems with poor purity and contamination. Here, we propose a green and sustainable lithium recovery strategy for spent batteries containing LiFePO4, LiCoO2, and LiNi0.5Co0.2Mn0.3O2 electrodes. Our proposed configuration of "lithium-rich electrode || LLZTO@LiTFSI+P3HT || LiOH" system achieves double-side and roll-to-roll recycling of lithium-containing electrode without destroying its integrity. The LiTFSI+P3HT-modified LLZTO membrane also solves the H+/Li+ exchange problem and realizes a waterproof protection of bare LLZTO in the aqueous working environment. On the basis of these advantages, our system shows high Li selectivity (97%) and excellent Faradaic efficiency (≥97%), achieving high-purity (99%) LiOH along with the production of H2. The Li extraction processes for spent LiFePO4, LiNi0.5Co0.2Mn0.3O2, and LiCoO2 batteries is shown to be economically feasible. Therefore, this study provides a previously unexplored technology with low energy consumption as well as high economic and environmental benefits to realize sustainable lithium recycling from spent batteries.

A synergistic exploitation to produce high-voltage quasi-solid-state lithium metal batteries.

The current Li-based battery technology is limited in terms of energy contents. Therefore, several approaches are considered to improve the energy density of these energy storage devices. Here, we report the combination of a heteroatom-based gel polymer electrolyte with a hybrid cathode comprising of a Li-rich oxide active material and graphite conductive agent to produce a high-energy "shuttle-relay" Li metal battery, where additional capacity is generated from the electrolyte's anion shuttling at high voltages. The gel polymer electrolyte, prepared via in situ polymerization in an all-fluorinated electrolyte, shows adequate ionic conductivity (around 2 mS cm-1 at 25 °C), oxidation stability (up to 5.5 V vs Li/Li+), compatibility with Li metal and safety aspects (i.e., non-flammability). The polymeric electrolyte allows for a reversible insertion of hexafluorophosphate anions into the conductive graphite (i.e., dual-ion mechanism) after the removal of Li ions from Li-rich oxide (i.e., rocking-chair mechanism).

Improved Sodiation Additive and Its Nuances in the Performance Enhancement of Sodium-Ion Batteries.

The abundance of the available sodium sources has led to rapid progress in sodium-ion batteries (SIBs), making them potential candidates for immediate replacement of lithium-ion batteries (LIBs). However, commercialization of SIBs has been hampered by their fading efficiency due to the sodium consumed in the formation of solid-electrolyte interphase (SEI) when using hard carbon (HC) anodes. Herein, Na2C3O5 sodium salt is introduced as a highly efficient, cost-effective, and safe cathode sodiation additive. This sustainable sodium salt has an oxidation potential of ∼4.0 V vs Na+/Na°, so it could be practically implemented into SIBs. Moreover, for the first time, we have also revealed by X-ray photoelectron spectroscopy (XPS) that in addition to the compensating Na+ ions spent in the SEI layer, the high specific capacity and capacity retention observed from electrochemical measurements are due to the formation of a thinner and more stable cathode-electrolyte interphase (CEI) on the P2-Na2/3Mn0.8Fe0.1Ti0.1O2 while using such a cathode sodiation additive. Half-cell studies with P2-Na2/3Mn0.8Fe0.1Ti0.1O2 cathodes show a 27% increase in the specific capacity (164 mAh gP2-1) with cathode sodiation additives. Full-cell studies with the HC anode show a 4 times increase in the specific capacity of P2-Na2/3Mn0.8Fe0.1Ti0.1O2. This work provides notable insights into and avenues toward the development of SIBs.

Immunizing lithium metal anodes against dendrite growth using protein molecules to achieve high energy batteries.

The practical applications of lithium metal anodes in high-energy-density lithium metal batteries have been hindered by their formation and growth of lithium dendrites. Herein, we discover that certain protein could efficiently prevent and eliminate the growth of wispy lithium dendrites, leading to long cycle life and high Coulombic efficiency of lithium metal anodes. We contend that the protein molecules function as a "self-defense" agent, mitigating the formation of lithium embryos, thus mimicking natural, pathological immunization mechanisms. When added into the electrolyte, protein molecules are automatically adsorbed on the surface of lithium metal anodes, particularly on the tips of lithium buds, through spatial conformation and secondary structure transformation from α-helix to ß-sheets. This effectively changes the electric field distribution around the tips of lithium buds and results in homogeneous plating and stripping of lithium metal anodes. Furthermore, we develop a slow sustained-release strategy to overcome the limited dispersibility of protein in the ether-based electrolyte and achieve a remarkably enhanced cycling performance of more than 2000 cycles for lithium metal batteries.

Polyolefin-Based Janus Separator for Rechargeable Sodium Batteries.

Rechargeable sodium batteries are a promising technology for low-cost energy storage. However, the undesirable drawbacks originating from the use of glass fiber membrane separators have long been overlooked. A versatile grafting-filtering strategy was developed to controllably tune commercial polyolefin separators for sodium batteries. The as-developed Janus separators contain a single-ion-conducting polymer-grafted side and a functional low-dimensional material coated side. When employed in room-temperature sodium-sulfur batteries, the poly(1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide sodium)-grafted side effectively enhances the electrolyte wettability, and inhibits polysulfide diffusion and sodium dendrite growth. Moreover, a titanium-deficient nitrogen-containing MXene-coated side electrocatalytically improved the polysulfide conversion kinetics. The as-developed batteries demonstrate high capacity and extended cycling life with lean electrolyte loading.

Symmetric All-Organic Battery Containing a Dual Redox-Active Polymer as Cathode and Anode Material.

All-organic batteries are a promising sustainable energy storage technology owing to the wide availability, flexibility, and recyclability of organic/polymeric compounds. The development of all-organic or polymer batteries is still a challenge, as both electrode materials need to be carefully optimized to have a wide difference of redox potential and compatibility with the electrolyte. Herein, dual redox-active polyimides based on phenothiazine and naphthalene tetracarboxylic dianhydride units are presented. After only one optimization step, the electrodes based on these dual redox polymers can be applied simultaneously as anode and cathode in a symmetric all-organic battery. The phenothiazine functional polyimide shows two redox active voltages at around 2.5 and 3.7 V (vs. Li/Li+ ) with high discharge capacities of 160 mAh g-1 . Moreover, the symmetric full battery delivers high power density up to 1542 W kg-1 with stable cyclability for 1000 cycles. This work demonstrates an efficient strategy to develop dual redox active polymer electrodes for next generation all-polymer batteries.

Stable Conversion Chemistry-Based Lithium Metal Batteries Enabled by Hierarchical Multifunctional Polymer Electrolytes with Near-Single Ion Conduction.

The low Coulombic efficiency and serious safety issues resulting from uncontrollable dendrite growth have severely impeded the practical applications of lithium (Li) metal anodes. Herein we report a stable quasi-solid-state Li metal battery by employing a hierarchical multifunctional polymer electrolyte (HMPE). This hybrid electrolyte was fabricated via in situ copolymerizing lithium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide (LiMTFSI) and pentaerythritol tetraacrylate (PETEA) monomers in traditional liquid electrolyte, which is absorbed in a poly(3,3-dimethylacrylic acid lithium) (PDAALi)-coated glass fiber membrane. The well-designed HMPE simultaneously exhibits high ionic conductivity (2.24×10-3  S cm-1 at 25 °C), near-single ion conducting behavior (Li ion transference number of 0.75), good mechanical strength and remarkable suppression for Li dendrite growth. More intriguingly, the cation permselective HMPE efficiently prevents the migration of negatively charged iodine (I) species, which provides the as-developed Li-I batteries with high capacity and long cycling stability.

A versatile functionalized ionic liquid to boost the solution-mediated performances of lithium-oxygen batteries.

Due to the high theoretical specific energy, the lithium-oxygen battery has been heralded as a promising energy storage system for applications such as electric vehicles. However, its large over-potentials during discharge-charge cycling lead to the formation of side-products, and short cycle life. Herein, we report an ionic liquid bearing the redox active 2,2,6,6-tetramethyl-1-piperidinyloxy moiety, which serves multiple functions as redox mediator, oxygen shuttle, lithium anode protector, as well as electrolyte solvent. The additive contributes a 33-fold increase of the discharge capacity in comparison to a pure ether-based electrolyte and lowers the over-potential to an exceptionally low value of 0.9 V. Meanwhile, its molecule facilitates smooth lithium plating/stripping, and promotes the formation of a stable solid electrolyte interface to suppress side-reactions. Moreover, the proportion of ionic liquid in the electrolyte influences the reaction mechanism, and a high proportion leads to the formation of amorphous lithium peroxide and a long cycling life (> 200 cycles). In particular, it enables an outstanding electrochemical performance when operated in air.

Two-Dimensional Unilamellar Cation-Deficient Metal Oxide Nanosheet Superlattices for High-Rate Sodium Ion Energy Storage.

Cation-deficient two-dimensional (2D) materials, especially atomically thin nanosheets, are highly promising electrode materials for electrochemical energy storage that undergo metal ion insertion reactions, yet they have rarely been achieved thus far. Here, we report a Ti-deficient 2D unilamellar lepidocrocite-type titanium oxide (Ti0.87O2) nanosheet superlattice for sodium storage. The superlattice composed of alternately restacked defective Ti0.87O2 and nitrogen-doped graphene monolayers exhibits an outstanding capacity of ∼490 mA h g-1 at 0.1 A g-1, an ultralong cycle life of more than 10000 cycles with ∼0.00058% capacity decay per cycle, and especially superior low-temperature performance (100 mA h g-1 at 12.8 A g-1 and -5 °C), presenting the best reported performance to date. A reversible Na+ ion intercalation mechanism without phase and structural change is verified by first-principles calculations and kinetics analysis. These results herald a promising strategy to utilize defective 2D materials for advanced energy storage applications.

A room-temperature sodium-sulfur battery with high capacity and stable cycling performance.

High-temperature sodium-sulfur batteries operating at 300-350 °C have been commercially applied for large-scale energy storage and conversion. However, the safety concerns greatly inhibit their widespread adoption. Herein, we report a room-temperature sodium-sulfur battery with high electrochemical performances and enhanced safety by employing a "cocktail optimized" electrolyte system, containing propylene carbonate and fluoroethylene carbonate as co-solvents, highly concentrated sodium salt, and indium triiodide as an additive. As verified by first-principle calculation and experimental characterization, the fluoroethylene carbonate solvent and high salt concentration not only dramatically reduce the solubility of sodium polysulfides, but also construct a robust solid-electrolyte interface on the sodium anode upon cycling. Indium triiodide as redox mediator simultaneously increases the kinetic transformation of sodium sulfide on the cathode and forms a passivating indium layer on the anode to prevent it from polysulfide corrosion. The as-developed sodium-sulfur batteries deliver high capacity and long cycling stability.

Highly Efficient, Cost Effective, and Safe Sodiation Agent for High-Performance Sodium-Ion Batteries.

The development of sodium-ion batteries has been hindered so far by the large irreversible capacity of hard carbon anodes and other anode materials in the initial few cycles, as sodium ions coming from cathode materials is consumed in the formation of the solid-electrolyte interface (SEI) and irreversibly trapped in anodes. Herein, the successful synthesis of an environmentally benign and cost-effective sodium salt (Na2 C4 O4 ) is reported that could be applied as additive in cathodes to solve the irreversible-capacity issues of anodes in sodium-ion batteries. When added to Na3 (VO)2 (PO4 )2 F cathode, the cathode delivered a highly stable capacity of 135 mAh g-1 and stable cycling performance. The water-stable Na3 (VO)2 (PO4 )2 F cathode in combination with a water-soluble sacrificial salt eliminates the need for using any toxic solvents for laminate preparation, thus paving way for greener electrode fabrication techniques. A 100 % increase in capacity of sodium cells (full-cell configuration) has been observed when using the new sodium salt at a C-rate of 2C. Regardless of the electrode fabrication technique, this new salt finds use in both aqueous and non-aqueous cathode-fabrication techniques for sodium-ion batteries.

A Stable Quasi-Solid-State Sodium-Sulfur Battery.

Ambient-temperature sodium-sulfur (Na-S) batteries are considered a promising energy storage system due to their high theoretical energy density and low costs. However, great challenges remain in achieving a high rechargeable capacity and long cycle life. Herein we report a stable quasi-solid-state Na-S battery enabled by a poly(S-pentaerythritol tetraacrylate (PETEA))-based cathode and a (PETEA-tris[2-(acryloyloxy)ethyl] isocyanurate (THEICTA))-based gel polymer electrolyte. The polymeric sulfur electrode strongly anchors sulfur through chemical binding and inhibits the shuttle effect. Meanwhile, the in situ formed polymer electrolyte with high ionic conductivity and enhanced safety successfully stabilizes the Na anode/electrolyte interface, and simultaneously immobilizes soluble Na polysulfides. The as-developed quasi-solid-state Na-S cells exhibit a high reversible capacity of 877 mA h g-1 at 0.1 C and an extended cycling stability.

New Redox Polymers that Exhibit Reversible Cleavage of Sulfur Bonds as Cathode Materials.

Two new cathode materials based on redox organosulfur polymers were synthesized and investigated for rechargeable lithium batteries as a proof-of-concept study. These cathodes offered good cycling performance owing to the absence of polysulfide solubility, which plagues Li/S systems. Herein, an aliphatic polyamine or a conjugated polyazomethine was used as the base to tether the redox-active species. The activity comes from the cleavage and formation of S-S or N-S bonds, which is made possible by the rigid conjugated backbone. The synthesized polymers were characterized through FTIR spectroscopy and thermogravimetric analysis (TGA). Galvanostatic measurements were performed to evaluate the discharge/charge cycles and characterize the performance of the lithium-based cells, which displayed initial discharge capacities of approximately 300 mA h g-1 at C/5 over 100 cycles with approximately 98 % Coulombic efficiency.

Hindered Glymes for Graphite-Compatible Electrolytes.

Organic carbonate mixtures are used almost exclusively as lithium battery electrolyte solvents. The linear compounds (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate) act mainly as thinner for the more viscous and high-melting ethylene carbonate but are the least stable component and have low flash points; these are serious handicaps for lifetime and safety. Polyethers (glymes) are useful co-solvents, but all formerly known representatives solvate Li(+) strongly enough to co-intercalate in the graphite negative electrode and exfoliate it. We have put forward a new electrolyte composition comprising a polyether to which a bulky tert-butyl group is attached ("hindered glyme"), thus completely preventing co-intercalation while maintaining good conductivity. This alkyl-carbonate-free electrolyte shows remarkable cycle efficiency of the graphite electrode, not only at room temperature, but also at 50 and 70 °C in the presence of lithium bis(fluorosulfonimide). The two-ethylene-bridge hindered glyme has a high boiling point and a flash point of 80 °C, a considerable advantage for safety.

Boron esters as tunable anion carriers for non-aqueous batteries electrochemistry.

Compounds like LiF, Li(2)O, and Li(2)O(2) have considerable importance in batteries; the first two are ubiquitous in the protective SEI at the negative electrode, or the result of conversion reactions with fluorides and oxides. The latter, Li(2)O(2,) forms from oxygen reduction in the much vaunted Li/air batteries. Mastering their solubility in Li-based electrolytes is viewed as essential for further progress in battery safety, lifetime, or capacity. Aprotic solvents cannot provide the H-bonds necessary to their dissolution, and simple practical solutions have yet to materialize. Here we disclose a novel and large family of boron esters of general formula Y-C((CH(2)O)(Z(1)O)(Z(2)O))B whose Lewis acidity stems from geometrical constraint and can be tuned via electron affinity either by Y = CH(3) --> Y = NO(2) or Z(1,2) = CH(2) --> Z(1,2) = CO so as to partially or fully dissolve the above compounds both in battery solvent EC/DMC and in DMF. The extreme simplicity of synthesis and variability of these boron-based anion carriers, where the exchange rate is fast, are not only a valuable addition to coordination science but also a step forward to improve present battery systems.