Bifunctional 1-Boc-3-Iodoazetidine Enhancing Lithium Anode Stability and Rechargeability of Lithium-Oxygen Batteries

A Redox Mediator Containing Reversible Dynamic Boron-Oxygen Bonds to Construct an Adaptive SEI Layer for Advanced Li-O2 Batteries

Lithium-oxygen (Li-O2) batteries have high theoretical energy density, but the discharge product Li2O2 of Li-O2 batteries is difficult to decompose, resulting in the undesirably high charging potential. The use of soluble redox mediators (RMs) can usually reduce the high charging potential of Li-O2 batteries, but the RM on the cathode side can diffuse to the Li metal anode and react with it, leading to continuous loss of the RM and causing damage to the fragile Li anode interface. So, it is necessary to develop a bifunctional redox mediator (BRM) that can simultaneously reduce the charging potential and protect the Li anode. Herein, we introduced 4-bromomethyl-phenylboronic acid (BPLA) as a BRM. The Br- ions can be dissociated from BPLA during cycling and serve as an effective component of RM, thereby significantly facilitating the reduction of charging potential of Li-O2 batteries. Meanwhile, the boronic acid groups in BPLA have the capability to engage in cross-linking reactions on the Li-metal surface, forming a flexible and continuous solid-electrolyte interphase (SEI) layer. More importantly, the SEI layer contains the reversible dynamic B-O covalent bond, which possesses a characteristic of continuous dissociation and rearrangement. Thereby the SEI layer possesses the shape adaptability, inhibits the growth of Li dendrites, and suppresses the reaction between RM and Li. Consequently, our BPLA, serving as the BRM, can enable Li-O2 batteries to achieve a stable cycle life of 180 cycles under the low charge potential up to 4.0 V.

A Bifunctional Imidazolyl Iodide Mediator of Electrolyte Boosts Cathode Kinetics and Anode Stability Towards Low Overpotential and Long-Life Li-O2 Batteries

The addition of a redox mediator as soluble catalyst into electrolyte can effectively overcome the bottlenecks of poor energy efficiency and limited cyclability for Li-O2 batteries caused by passivation of insulating discharge products and unfavorable byproducts. Herein we report a novel soluble catalyst of bifunctional imidazolyl iodide salt additive, 1,3-dimethylimidazolium iodide (DMII), to successfully construct highly efficient and durable Li-O2 batteries. The anion I- can effectively promote the charge transport of Li2O2 and accelerate the redox kinetics of oxygen reduction/oxygen evolution reactions on the cathode side, thereby significantly decreasing the charge/discharge overpotential. Simultaneously, the cation DMI+ forms an ultrathin stably solid-electrolyte interphase film on Li metal, greatly inhibiting the shuttle effect of I- and improving the stability of anode. Using this DMII additive, our Li-O2 batteries achieve an extremely low voltage of 0.52 V and ultra-long cycling stability over 960 h. Notably, up to 95.8 % of the Li2O2 yield further proves the reversible generation/decomposition of Li2O2 without the occurrence of side reactions. Both experimental and theoretical results disclose that DMII enables Li+ easily solvated, testifying the dominance of the solution-induced reaction mechanism. This work provides the possibility to design the soluble catalysts towards high-performance Li-O2 batteries.

Protecting Li-metal anode with LiF-enriched solid electrolyte interphase derived from a fluorinated graphene additive

As the holy-grail material, the Li-metal anode has been considered the potential anode of the next generation of Li-metal batteries (LMBs). However, issues of undesirable dendrite growth and unsatisfactory reversibility of the Li-plating/stripping process during the electrochemical cycling impede further application of LMBs. Herein, we innovatively introduce fluorinated graphene (F-Gr) species as a sacrificial effective electrolyte additive into EC/EMC-based electrolyte, which effectively triggers LiF-enriched (composition) and organic/inorganic species uniform-distributed (structure) SEI film architecture that features robustness and denseness, as well as good stability. With the F-Gr additive, efficient Li-metal anode protection (dendrite-free morphology on Li-metal surface and improved Li plating/stripping reversibility during electrochemical cycling) and significantly enhanced long-term lifespan of LMBs is achieved. Remarkably, classical electrochemical techniques, combined with the surface-sensitive characterizations (XPS and TOF-SIMS), comprehensively and systematically highlight critical structure-activity relationships between the SEI architecture (both composition and structure) and electrochemical performance. These techniques provide deep insights into the optimal electrolyte designation of Li-metal anode in LMBs.

Protecting Li-metal in O2 atmosphere by a sacrificial polymer additive in Li-O2 batteries

Li-O2 batteries (LOBs) with Li-metal as the anode are characterized by their high theoretical energy density of 3500 W h kg-1 and are thus considered next-generation batteries with an unlimited potential. However, upon cycling in a harsh O2 atmosphere, the poor-quality solid electrolyte interphase (SEI) film formed on the surface of the Li-metal anode cannot effectively suppress the shuttle effect from O2, superoxide species, protons, and soluble side products. These issues lead to aggravated Li-metal corrosion and hinder the practical development of LOBs. In this work, a polyacrylamide-co-polymethyl acrylate (PAMMA) copolymer was innovatively introduced in an ether-based electrolyte as a sacrificial additive. PAMMA was found to preferentially decompose and promote the formation of a dense and Li3N-rich SEI film on the Li-metal surface, which could effectively prohibit the shuttle effect from a series of detrimental species in the Li-O2 cell during the discharge/charge process. Using PAMMA, well-protected Li-metal in a harsh O2 atmosphere and significantly enhanced cycling performance of the Li-O2 cell could be achieved. Thus, the use of a sacrificial polymer additive provides a promising strategy for the effective protection of Li-metal in Li-O2 cells in a severe O2 atmosphere during practical applications.

In Situ Construction of a Multifunctional Interface Regulator with Amino-Modified Conjugated Diene toward High-Rate and Long-Cycle Silicon Anodes

Silicon (Si) is deemed to be the next-generation lithium-ion battery anode. However, on account of the poor electronic conductivity of Si materials and the instability of the solid electrolyte interphase layer, the electrochemical performance of Si anodes is far from reaching the application level. In this work, a multifunctional poly(propargylamine) (PPA) interlayer is constructed on the Si surface via a simple in situ polymerization method. Benefiting from the electronic conductivity, ionic conductivity, robust interphase interactions for hydrogen bonding, and stability of multifunctional PPA, the optimized Si@PPA-7% electrode shows improved lithium storage capability. A high capacity of 1316.3 mAh g^-1 is retained after 500 cycles at 2.1 A g^-1, and 2370.3 mAh g^-1 can be delivered at 42 A g^-1, which are in stark contrast to the unmodified Si electrode. Furthermore, the rate and cycle capabilities of the LiFePO₄//Si@PPA-7% full cell are also obviously better than those of LiFePO₄//Si.

Adjusting the Covalency of Metal-Oxygen Bonds in LaCoO3 by Sr and Fe Cation Codoping to Achieve Highly Efficient Electrocatalysts for Aprotic Lithium-Oxygen Batteries

Developing high-efficiency dual-functional catalysts to promote oxygen electrode reactions is critical for achieving high-performance aprotic lithium-oxygen (Li-O₂) batteries. Herein, Sr and Fe cation-codoped LaCoO₃ perovskite (La_0.8Sr_0.2Co_0.8Fe_0.2O_3-σ, LSCFO) porous nanoparticles are fabricated as promising electrocatalysts for Li-O₂ cells. The results demonstrate that the LSCFO-based Li-O₂ batteries exhibit an extremely low overpotential of 0.32 V, ultrahigh specific capacity of 26 833 mA h g^-1, and superior long-term cycling stability (200 cycles at 300 mA g^-1). These prominent performances can be partially attributed to the existence of abundant coordination unsaturated sites caused by oxygen vacancies in LSCFO. Most importantly, density functional theory (DFT) calculations reveal that codoping of Sr and Fe cations in LaCoO₃ results in the increased covalency of Co 3d-O 2p bonds and the transition of Co³⁺ from an ordinary low-spin state to an intermediate-spin state, eventually resulting in the transformation from nonconductor LCO to metallic LSCFO. In addition, based on the theoretical calculations, it is found that the inherent adsorption capability of LSCFO toward the LiO₂ intermediate is reduced due to the increased covalency of Co 3d-O 2p bonds, leading to the formation of large granule-like Li₂O₂, which can be effectively decomposed on the LSCFO surface during the charging process. Notably, this work demonstrates a unique insight into the design of advanced perovskite oxide catalysts via adjusting the covalency of transition-metal-oxygen bonds for high-performance metal-air batteries.