Mengya Li

Solid‐state batteries (SSBs), particularly those utilizing sodium metal, are emerging as a promising technology due to their potential for enhanced safety, higher energy density, and longer cycle life. NASICON (Na superionic conductor) materials, known for their robust crystalline structure and high ionic conductivity, are pivotal in the development of efficient sodium all‐solid‐state batteries. These materials exhibit high room‐temperature ionic conductivity and electrochemical stability, making them ideal for various applications. Research has focused on improving NASICON's ionic conductivity and stability through doping, interface regulation, and composite anode design. Recent advancements include Ti‐doped Na₃Zr₂Si₂PO₁₂ (Ti‐NZSP), which demonstrates improved surface stability, higher ionic conductivity, and increased critical current density. However, challenges such as Na dendrite formation and mechanical integrity under operational conditions persist. Advanced imaging techniques like operando synchrotron X‐ray tomography have provided insights into failure mechanisms, revealing that pore‐filling and dendrite growth are significant issues. Understanding these processes is essential for enhancing the performance and safety of Na‐based SSBs. This study underscores the need for continued research to address these challenges and develop reliable, high‐performance solid‐state electrolytes for future energy storage solutions.

Li-ion battery degradation and safety events are often attributed to undesirable metallic lithium plating. Since their release, Li-ion battery electrodes have been made progressively thicker to provide a higher energy density. However, the propensity for plating in these thicker pairings is not well understood. Herein, we combine an experimental plating-prone condition with robust mesoscale modeling to examine electrode pairings with capacities ranging from 2.5 to 6 mAh/cm² and negative to positive (N/P) electrode areal capacity ratio from 0.9 to 1.8 without the need for extensive aging tests. Using both experimentation and a mesoscale model, we identify a shift from conventional high state-of-charge (SOC) type plating to high overpotential (OP) type plating as electrode thickness increases. These two plating modes have distinct morphologies, identified by optical microscopy and electrochemical signatures. We demonstrate that under operating conditions where these plating modes converge, a high propensity of plating exists, revealing the importance of predicting and avoiding this overlap for a given electrode pairing. Further, we identify that thicker electrodes, beyond a capacity of 3 mAh/cm² or thickness >75 μm, are prone to high OP, limiting negative electrode (NE) utilization and preventing cross-sectional oversizing the NE from mitigating plating. Here, it simply contributes to added mass and volume. The experimental thermal gradient and mesoscale model either combined or independently provide techniques capable of probing performance and safety implications of mild changes to electrode design features.

Sodium-ion batteries (SIBs) have emerged as promising alternatives to their lithium-ion counterparts due to the abundance of sodium resources and their potential for cost-effective energy storage solutions. The chemistry for SIBs has been investigated since the 1980s, but it went through a slow research and development process. Recently, there has been an acceleration in technology maturation due to a supply chain crisis originating from unequal resource distribution and sustainability and safety concerns regarding lithium-ion batteries. However, the practical application of SIBs has been hindered primarily by challenges related to cathode materials, specifically, surface and structural stabilities in different conditions. Through the integration of advanced techniques such as in situ spectroscopy, operando diffraction, and high-resolution microscopy, a comprehensive understanding of the cathode’s dynamic behavior and degradation mechanisms can be achieved. The identified structural modifications, phase transitions, and degradation pathways offer critical insights into the design of robust cathode materials with prolonged cycling stability, fast charging capability, high energy density, great low-temperature performance, and safety. This review underscores the pivotal role of cutting-edge characterization techniques in guiding the development of high-performance sodium-ion batteries, thereby fostering the realization of sustainable and efficient energy storage solutions for diverse technological applications.

Reversible lattice oxygen redox reactions offer the potential to enhance energy density and lower battery cathode costs. However, their widespread adoption faces obstacles like substantial voltage hysteresis and poor stability. The current research addresses these challenges by achieving a non-hysteresis, long-term stable oxygen redox reaction in the P3-type Na_2/3Cu_1/3Mn_2/3O₂. Here we show this is accomplished by forming spin singlet states during charge and discharge. Detailed analysis, including in-situ X-ray diffraction, shows highly reversible structural changes during cycling. In addition, local CuO₆ Jahn-Teller distortions persist throughout, with dynamic Cu-O bond length variations. In-situ hard X-ray absorption and ex-situ soft X-ray absorption study, along with density function theory calculations, reveal two distinct charge compensation mechanisms at approximately 3.66 V and 3.99 V plateaus. Notably, we observe a Zhang-Rice-like singlet state during 3.99 V charging, offering an alternative charge compensation mechanism to stabilize the active oxygen redox reaction.

Ni-rich LiNi_xMn_yCo_1−x−yO₂ (NMC) materials have been adopted in a range of applications, including electric vehicles. The recycled NMC material from a spent cell would be much more valuable if it could be upgraded to a Ni-rich, more energy-dense version of the material. This work demonstrates a simple, inexpensive, and facile method to upcycle LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111, 160 mAh∙g⁻¹), a cathode used in early generations of electric vehicle batteries, to LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811, 190 mAh∙g⁻¹), a more energy-dense cathode material. In this study, a preliminary investigation into a room-temperature eutectic synthesis of NMC811 is performed using NMC111, LiOH, and nickel nitrate as precursors. The synthesized material showed the desired crystal structure and stoichiometry, though the cycle life and Li diffusion coefficient need improvement when compared to commercially available NMC811. This study demonstrates an interesting proof of concept of the room-temperature eutectic synthesis process for LIB cathodes and could be improved by tuning the synthesis conditions.

Conventional sodium‐based layered oxide cathodes are extremely air sensitive and possess poor electrochemical performance along with safety concerns when operating at high voltage. The polyanion phosphate, Na₃V₂(PO₄)₃ stands out as an excellent candidate due to its high nominal voltage, ambient air stability, and long cycle life. The caveat is that Na₃V₂(PO₄)₃ can only exhibit reversible capacities in the range of 100 mAh g⁻¹, 20% below its theoretical capacity. Here, the synthesis and characterizations are reported for the first time of the sodium‐rich vanadium oxyfluorophosphate, Na_3.2Ni_0.2V_1.8(PO₄)₂F₂O, a tailored derivative compound of Na₃V₂(PO₄)₃, with extensive electrochemical and structural analyses. Na_3.2Ni_0.2V_1.8(PO₄)₂F₂O delivers an initial reversible capacity of 117 mAh g⁻¹ between 2.5 and 4.5 V under the 1C rate at room temperature, with 85% capacity retention after 900 cycles. The cycling stability is further improved when the material is cycled at 50 °C within 2.8–4.3 V for 100 cycles. When paired with a presodiated hard carbon, Na_3.2Ni_0.2V_1.8(PO₄)₂F₂O cycled with a capacity retention of 85% after 500 cycles. Cosubstitution of the transition metal and fluorine in Na_3.2Ni_0.2V_1.8(PO₄)₂F₂O as well as the sodium‐rich structure are the major factors behind the improvement of specific capacity and cycling stability, which paves the way for this cathode in sodium‐ion batteries.