An entanglement association polymer electrolyte for Li-metal batteries.

To improve the interface stability between Li-rich Mn-based oxide cathodes and electrolytes, it is necessary to develop new polymer electrolytes. Here, we report an entanglement association polymer electrolyte (PVFH-PVCA) based on a poly (vinylidene fluoride-co-hexafluoropropylene) (PVFH) matrix and a copolymer stabilizer (PVCA) prepared from acrylonitrile, maleic anhydride, and vinylene carbonate. The entangled structure of the PVFH-PVCA electrolyte imparts excellent mechanical properties and eliminates the stress arising from dendrite growth during cycling and forms a stable interface layer, enabling Li//Li symmetric cells to cycle steadily for more than 4500 h at 8 mA cm-2. The PVCA acts as a stabilizer to promote the formation of an electrochemically robust cathode-electrolyte interphase. It delivers a high specific capacity and excellent cycling stability with 84.7% capacity retention after 400 cycles. Li1.2Mn0.56Ni0.16Co0.08O2/PVFH-PVCA/Li full cell achieved 125 cycles at 1 C (4.8 V cut-off) with a stable discharge capacity of ~2.5 mAh cm-2.

An Ultrasmall Ordered High-Entropy Intermetallic with Multiple Active Sites for the Oxygen Reduction Reaction.

Controlling multimetallic ensembles at the atomic level is significantly challenging, particularly for high-entropy alloys with more than five elements. Herein, we report an innovative ultrasmall (∼2 nm) PtFeCoNiCuZn high-entropy intermetallic (PFCNCZ-HEI) with a well-ordered structure synthesized by using the space-confined strategy. By exploiting these combined metals, the PFCNCZ-HEI nanoparticles achieve an ultrahigh mass activity of 2.403 A mgPt-1 at 0.90 V vs reversible hydrogen electrode for the oxygen reduction reaction, which is up to 19-fold higher than that of state-of-the-art commercial Pt/C. A proton exchange membrane fuel cell assembled with PFCNCZ-HEI as the cathode (0.03 mgPt cm-2) exhibits a power density of 1.4 W cm-2 and a high mass-normalized rated power of 45 W mgPt-1. Furthermore, theoretical calculations reveal that the outer electrons of the non-noble-metal atoms on the surface of the PFCNCZ-HEI nanoparticle are modulated to show characteristics of multiple active centers. This work offers a promising catalyst design direction for developing highly ordered HEI nanoparticles for electrocatalysis.

Unlocking the Potential of Li-Rich Mn-Based Oxides for High-Rate Rechargeable Lithium-Ion Batteries.

Lithium-rich Mn-based oxides have gained significant attention worldwide as potential cathode materials for the next generation of high-energy density lithium-ion batteries. Nonetheless, the inferior rate capability and voltage decay issues present formidable challenges. Here, a Li-rich material equipped with quasi-three-dimensional (quasi-3D) Li-ion diffusion channels is initially synthesized by introducing twin structures with high Li-ion diffusion coefficients into the crystal and constructing a "bridge" between different Li-ion diffusion tunnels. The as-prepared material exhibits monodispersed micron-sized primary particles (MP), delivering a specific capacity of 303 mAh g-1 at 0.1 C and an impressive capacity of 253 mAh g-1 at 1 C. More importantly, the twin structure also serves as a "breakwater" to inhibit the migration of Mn ions and improve the overall structural stability, leading to cycling stability with 85% capacity retention at 1 C after 200 cycles. The proposed strategy of constructing quasi-3D channels in the layered Li-rich cathodes will open up new avenues for the research and development of other layered oxide cathodes, with potential applications in industry.

PtFeCoNiCu high-entropy solid solution alloy as highly efficient electrocatalyst for the oxygen reduction reaction.

Searching for an efficient, durable, and low cost catalyst toward oxygen reduction reaction (ORR) is of paramount importance for the application of fuel cell technology. Herein, PtFeCoNiCu high-entropy alloy nanoparticles (PFCNC-HEA) is reported as electrocatalyst toward ORR. It shows remarkable ORR catalytic mass activity of 1.738 A mg-1 Pt at 0.90 V, which is 15.8 times higher than that of the state-of-art commercial Pt/C catalyst. It also exhibits outstanding stability with negligible voltage decay (3 mV) after 10k cycles accelerated durability test. High ORR activity is ascribed to the ligand effect caused by polymetallic elements, the optimization of the surface electronic structure, and the formation of multiple active sites on the surface. In the proton exchange membrane fuel cell setup, this cell delivers a power density of up to 1.380 W cm-2 with a cathodic Pt loading of 0.03 mgPt cm-2, demonstrating a promising catalyst design direction for highly efficient ORR.

Entropy Stabilization Strategy for Enhancing the Local Structural Adaptability of Li-Rich Cathode Materials.

Layered Li-rich cathode materials with high reversible energy densities are becoming prevalent. However, owing to the activation of low-potential redox couples and the progressively irreversible structural transformation caused by the local adjustment of transition-metal ions in the intra/interlayer driven by anionic redox, continuous capacity degradation, and voltage decay emerge, thus greatly reducing the energy density and increasing the difficulty of battery system management. Herein, layered Li-rich cathode materials with higher intralayer configuration entropy have more local structural diversity and higher distortion energy, resulting in superior local structural adaptability with no drastic redox couple evolution, major local structural adjustment, or obvious layered-to-spinel phase transition. Consequently, the energy retention of the entropy-stabilization-strategy-enhanced Li-rich cathode materials is almost twice that of a typical Li-rich cathode material (Li1.20 Mn0.54 Ni0.13 Co0.13 O2 , T-LRM) after 3 months of cyclic testing. Moreover, when cycled at 1 C, the voltage degradation per cycle is less than 0.02%, that is, it results in a voltage loss of only 0.8 mV per cycle, which is excellent performance. This study paves the way for the development of Li-rich cathode materials with stabilized intralayer atomic arrangements and high local structural adaptability.

Sulfuration of Li-Rich Mn-Based Cathode Materials for Multianionic Redox and Stabilized Coordination Environment.

Lithium-rich transition metal oxides (LLOs) can deliver high specific capacity over 250 mAh g-1 , stemming from additional contribution of oxygen redox. However, the formation of O(2- n )- (0 < n < 2) species and even oxygen gas during the deep oxidation stage leads to progressive structural transformation that cause voltage decay/hysteresis, sluggish kinetics, and poor thermostability, preventing real-world application of LLOs. Therefore, the substantive key relies on enhancing the anionic redox stability in LLOs. Here, a sulfuration procedure of LLOs (S-LLOs) is proposed, in which sulfur anions are incorporated into oxygen sites in the lattice structure and form polyanions on the surface. Proved by structural characterizations and density functional theory (DFT) calculations, sulfur anions in the interior lattice can reversibly participate in the redox process and enhance the integral coordination stability by mitigating undesired oxygen redox. Moreover, S polyanions at the surface form a protecting layer for interfacial stability. The electrochemical measurements indicate that S-LLO demonstrates a high discharge capacity of 307.8 mAh g-1 , an outstanding capacity retention rate of 91.5% after 200 cycles, along with excellent voltage maintenance, rate capability, and thermostability. The sulfuration process of LLOs with multianionic redox mechanism highlights a promising strategy to design novel high-energy-density cathode materials with superior cycling performance.