A flame-retardant binder with high polysulfide affinity for safe and stable lithium–sulfur batteries

Lithium-sulfur(Li-S) batteries have shown promises for the next-generation, high-energy electrochemical storage, yet are hindered by rapid performance decay due to the polysulfide shuttle in the cathode and safety concerns about potential thermal runaway. To address the above challenges, herein, we show a flame-retardant cathode binder that simultaneously improves the electrochemical stability and safety of batteries. The combination of soft and hard segments in the polymer framework of binders allows high flexibility and mechanical strength for adapting to the drastic volume change during the Li(de)intercalation of the S cathode. The binder contains a large number of polar groups, which show the high affinity to polysulfides so that they help to anchor active S species at the cathode. These polar groups also help to regulate and facilitate the Li-ion transport, promoting the kinetics of polysulfide conversion reaction. The binder contains abundant phosphine oxide groups, which, in the case of battery's thermal runaway, decompose and release PO· radicals to quench the combustion reactions and stop the fire. Consequently, Li-S batteries using the new cathode binder show the improved electrochemical performance, including a low-capacity decay of 0.046% per cycle for 800 cycles at 1 C and favorable rate capabilities of up to 3 C. This work offers new insights on the practical realization of high-energy rechargeable batteries with stable storage electrochemistry and high safety.

Large-Scale Synthesis of the Stable Co-Free Layered Oxide Cathode by the Synergetic Contribution of Multielement Chemical Substitution for Practical Sodium-Ion Battery

The O3-type layered oxide cathodes for sodium-ion batteries(SIBs)are considered as one of the most promising systems to fully meet the requirement for future practical application.However,fatal issues in several respects such as poor air stability,irreversible complex multiphase evolution,inferior cycling lifespan,and poor industrial feasibility are restricting their commercialization development.Here,a stable Co-free O3-type NaNi_(0.4)Cu_(0.05)Mg_(0.05)Mn_(0.4)Ti_(0.1O2) cathode material with large-scale production could solve these problems for practical SIBs.Owing to the synergetic contribution of the multielement chemical substitution strategy,this novel cathode not only shows excellent air stability and thermal stability as well as a simple phase-transition process but also delivers outstanding battery performance in half-cell and full-cell systems.Meanwhile,various advanced characterization techniques are utilized to accurately decipher the crystalline formation process,atomic arrangement,structural evolution,and inherent effect mechanisms.Surprisingly,apart from restraining the unfavorable multiphase transformation and enhancing air stability,the accurate multielement chemical substitution engineering also shows a pinning effect to alleviate the lattice strains for the high structural reversibility and enlarges the interlayer spacing reasonably to enhance Na^(+)diffusion,resulting in excellent comprehensive performance.Overall,this study explores the fundamental scientific understandings of multielement chemical substitution strategy and opens up a new field for increasing the practicality to commercialization.