Zhao Chen

Amorphous halide solid electrolytes (AHSEs) have emerged as promising candidates for high-performance all-solid-state Na batteries (ASSNBs) owing to their balanced comprehensive performance. However, rational design principles assisting the precursor selection are still limited for developing low-cost Na-based AHSEs with improved ionic conductivity. Herein, a series of low-cost AHSEs, xNaBF4–ZrCl4 (x = 0.3, 0.5, 1, and 2), were synthesized via a one-step mechanochemical process. Competitive coordination between the Zr4+ and B3+ cations under mechanochemical activation is proposed to promote the rearrangement of F– and Cl– anions within the halide framework. The resulting dual-distorted polyhedral coordination facilitates the formation of long-range disordered structures that are highly favorable for isotropic Na+ transport, exhibiting a high Na+ ionic conductivity up to 1.01 mS cm–1 at 30 °C with excellent oxidative stability of 4.33 V vs Na+/Na. When assembled into all-solid-state cells, the 0.5NaBF4–ZrCl4 electrolyte enables stable cycling between 2.5 and 4.2 V with a capacity retention of 71.5% after 400 cycles at 0.2 C rate. This work provides a novel design paradigm for AHSEs and highlights the promising potential of high-performance ASSNBs.

Mn-rich phosphate of Na3.3Mn1.15Ti0.85(PO4)3 (NMTP), only containing high-abundance elements, was considered a promising cathode for Na-ion batteries (NIBs) owing to its 2.3-electron reactions and high working voltage based on Mn2+/Mn3+/Mn4+ redox couples between 2.5 and 4.2 V. However, excessive Mn content provides more chances for Mn2+ delocalization to sodium vacancies (Mn/Na□) to generate intrinsic antisite defects (IASDs), which leads to more serious voltage hysteresis in charge/discharge profiles, limiting the energy density of the NMTP system. Herein, we propose to introduce dopants with low valence and electronegativity into the titanium sites of NMTP to regulate Mn–O coordination chemistry. Following this rule, monovalent and low-electronegativity Li+ dopants are selected to build an enhanced Mn–O framework with a Na-rich environment, effectively reducing Mn/Na□ IASDs during the synthesis of materials. Benefited from facilitated Na+ diffusion kinetics because of the less Mn/Na□ IASD-affected pathway in the structure, Li+-doped NMTP (NMTLiP) shows suppressed voltage hysteresis behavior, achieving an energy density increase from 331 to 426 W h kg–1. This current work provides directional guidance from a coordination chemistry regulation perspective to suppress structure defects in Mn-rich phosphate cathodes toward high-energy NIBs.

Safety is a fundamental criterion for determining rechargeable batteries in energy storage applications1,2. Despite the great efforts in non-flammable electrolytes, they still cannot achieve intrinsic safety so far in Ah-level batteries without thermal runaway3-10, and the relationship between the flame-retardancy of electrolytes and the safety performance of batteries is still unclear. Here, we propose a polymerizable and non-flammable electrolyte (PolyNonflyte or PNE). In addition to the inherent non-flammability, this formulation also leverages the synergistic anion-cation solvation effect and undergoes thermally triggered polymerization, facilitating the optimized electrode-electrolyte interfacial chemistry and a cross-linked barrier that prevents mechanical/chemical interactions between the electrodes with impeded side reactions and reductive gases generation. These features promise PNE to eliminate thermal runaway in Ah-level cylindrical cells even when the temperature rises to 300°C in accelerating rate calorimeter and thermal abuse tests. The nail penetration tests were also passed without fire, smoke, or explosion. Furthermore, batteries with this electrolyte exhibit exceptional temperature adaptability between -40°C and 60°C and a high energy density of 211 Wh/kg at 4.3 V. This work brings a new insight of the battery safety beyond non-flammable electrolyte design and paves the way towards safer and more efficient battery systems for energy storage technology.

Prussian blue analogues (PBAs) are promising cathode candidates for aqueous Na ion batteries (ANIBs) considering their low-carbon and cost-effective features. However, it is still a huge challenge to achieve desirable energy density coupled with long cycle life due to inherent Na defects in PBAs and the unstable solid-electrolyte interphase (SEI) layer. Herein, we design Na₂C₄O₄ additives as sodium supplements to compensate for Na defects in PBAs, while utilizing the CO₂ products decomposed from Na₂C₄O₄ to construct a robust SEI layer containing Na₂CO₃ species. As proof of concept, our building of full ANIBs using iron-based PBAs and NaTi₂(PO₄)₃ anode with an appropriate amount of Na₂C₄O₄ enable a reversible capacity of ∼144 mA h g^-1 at 0.2 C and an excellent cycling stability of 15,000 cycles with 85% retention at 10 C. The proposed concept is further extended to the manganese-based PBA ANIBs to deliver an energy density of 92 W h kg^-1 with improved cycling stability.