新型安全高性能固态锂离子电池材料问世

All-solid-state lithium-ion (Li-ion) batteries with solid electrolytes are non-flammable and have higher energy density and transference numbers than those with liquid electrolytes. They are expected to take a share of the market for conventional liquid electrolyte Li-ion batteries, such as electric vehicles. However, despite these advantages, solid electrolytes have lower Li-ion conductivity and pose challenges in achieving adequate electrode-solid electrolyte contact. While sulfide-based solid electrolytes are conductive, they react with moisture to form toxic hydrogen disulfide. Therefore, there's a need for non-sulfide solid electrolytes that are both conductive and stable in air to make safe, high-performance, and fast-charging solid-state Li-ion batteries.
采用固体电解质的全固态锂离子电池不易燃，且比液态电解质电池具有更高的能量密度和迁移数。它们有望在电动汽车等传统液态电解质锂离子电池市场中占据一席之地。然而，尽管存在这些优势，固体电解质的锂离子电导率较低，且在实现电极与固体电解质充分接触方面存在挑战。虽然硫化物基固体电解质具有导电性，但它们会与水分反应生成有毒的硫化氢。因此，需要既导电又在空气中稳定的非硫化物固体电解质，以制造安全、高性能和快速充电的固态锂离子电池。

In a recent study published in Chemistry of Materialson 28 March 2024, a research team led by Professor Kenjiro Fujimoto, Professor Akihisa Aimi from Tokyo University of Science, and Dr. Shuhei Yoshida from DENSO CORPORATION, discovered a stable and highly conductive Li-ion conductor in the form of a pyrochlore-type oxyfluoride.
在2024年3月28日发表于《Chemistry of Materials》的一项研究中，由东京理科大学教授Kenjiro Fujimoto、Akihisa Aimi以及株式会社电装（DENSO CORPORATION）的Shuhei Yoshida博士领导的研究团队发现了一种稳定且高导电性的烧绿石型氧氟化物锂离子导体。

According to Prof. Fujimoto, "Making all-solid-state lithium-ion secondary batteries has been a long-held dream of many battery researchers. We have discovered an oxide solid electrolyte that is a key component of all-solid-state lithium-ion batteries, which have both high energy density and safety. In addition to being stable in air, the material exhibits higher ionic conductivity than previously reported oxide solid electrolytes."
据藤本教授介绍，“制造全固态锂离子二次电池是许多电池研究人员长期以来的梦想。我们发现了一种氧化物固体电解质，它是兼具高能量密度与安全性的全固态锂离子电池的关键组件。这种材料不仅能在空气中保持稳定，其离子导电率也高于此前报道的氧化物固体电解质。”

The pyrochlore-type oxyfluoride studied in this work can be denoted as Li_2-xLa_(1+x)/3M₂O₆F (M = Nb, Ta). It underwent structural and compositional analysis using various techniques, including X-ray diffraction, Rietveld analysis, inductively coupled plasma optical emission spectrometry, and selected-area electron diffraction. Specifically, Li1.25La0.58Nb2O6F was developed, demonstrating a bulk ionic conductivity of 7.0 mS cm⁻¹ and a total ionic conductivity of 3.9 mS cm⁻¹ at room temperature. It was found to be higher than the lithium-ion conductivity of known oxide solid electrolytes. The activation energy of ionic conduction of this material is extremely low, and the ionic conductivity of this material at low temperature is one of the highest among known solid electrolytes, including sulfide-based materials.
本研究涉及的烧绿石型氧氟化物可表示为Li La M O F（M = Nb, Ta）。通过X射线衍射、Rietveld分析、电感耦合等离子体发射光谱和选区电子衍射等技术，对其结构和成分进行了分析。特别开发出的Li1.25La0.58Nb2O6F在室温下体离子电导率为7.0 mS cm⁻¹，总离子电导率达3.9 mS cm⁻¹，其锂离子电导率高于已知氧化物固体电解质。该材料的离子传导活化能极低，其低温下的离子电导率是已知固体电解质（包括硫化物基材料）中最高的之一。

Exactly, even at -10°C, the new material has the same conductivity as conventional oxide-based solid electrolytes at room temperature. Furthermore, since conductivity above 100 °C has also been verified, the operating range of this solid electrolyte is -10 °C to 100 °C. Conventional lithium-ion batteries cannot be used at temperatures below freezing. Therefore, the operating conditions of lithium-ion batteries for commonly used mobile phones are 0 °C to 45 °C.
确实，即使在零下10°C，这种新材料的导电性能也与传统氧化物基固体电解质在室温下的表现相当。此外，由于其在100°C以上的导电性也得到了验证，这种固体电解质的工作温度范围为-10°C至100°C。传统的锂离子电池无法在零度以下使用。因此，常用手机锂离子电池的工作条件为0°C至45°C。

The Li-ion conduction mechanism in this material was investigated. The conduction path of pyrochlore-type structure cover the F ions located in the tunnels created by MO₆ octahedra. The conduction mechanism is the sequential movement of Li-ions while changing bonds with F ions. Li ions move to the nearest Li position always passing through metastable positions. Immobile La³⁺ bonded to F ion inhibits the Li-ion conduction by blocking the conduction path and vanishing the surrounding metastable positions.
研究了该材料中的锂离子传导机制。烧绿石型结构的传导路径覆盖了位于由MO八面体形成的隧道中的F离子。传导机制是锂离子在与F离子改变键合的同时顺序移动。锂离子总是通过亚稳态位置移动到最近的锂位置。与F离子键合的固定La通过阻塞传导路径和消除周围的亚稳态位置来抑制锂离子传导。

Unlike existing lithium-ion secondary batteries, oxide-based all solid-state batteries have no risk of electrolyte leakage due to damage and no risk of toxic gas generation as with sulfide-based batteries. Therefore, this new innovation is anticipated to lead future research. "The newly discovered material is safe and exhibits higher ionic conductivity than previously reported oxide-based solid electrolytes. The application of this material is promising for the development of revolutionary batteries that can operate in a wide range of temperatures, from low to high," envisions Prof. Fujimoto. "We believe that the performance required for the application of solid electrolytes for electric vehicles is satisfied."
与现有的锂离子二次电池不同，氧化物基全固态电池因损坏导致电解液泄漏的风险为零，也不会像硫化物基电池那样产生有毒的燃料费。因此，这一新创新有望引领未来研究。藤本教授展望道："这种新发现的材料安全性高，且离子电导率高于此前报道的氧化物基固体电解质。该材料的应用有望开发出革命性电池，可在从低温到高温的广泛温度范围内工作。"我们相信，电动汽车应用固体电解质所需的性能已经满足。

Notably, the new material is highly stable and will not ignite if damaged. It is suitable for airplanes and other places where safety is critical. It is also suitable for high-capacity applications, such as electric vehicles, because it can be used under high temperatures and supports rapid recharging. Moreover, it is also a promising material for miniaturization of batteries, home appliances, and medical devices.
值得注意的是，这种新材料高度稳定，即使受损也不会起火。它适用于飞机等安全至上的场所，也适用于电动汽车等高容量应用场景，因为它能在高温下使用并支持快速充电。此外，该材料在电池、家电和医疗设备的小型化领域同样具有广阔前景。

In summary, researchers have not only discovered a Li-ion conductor with high conductivity and air stability but also introduced a new type of superionic conductor with a pyrochlore-type oxyfluoride. Exploring the local structure around lithium, their dynamic changes during conduction, and their potential as solid electrolytes for all-solid-state batteries are important areas for future research!
总之，研究人员不仅发现了一种具有高电导率和空气稳定性的锂离子导体，还引入了一种新型的烧绿石型氧氟化物超离子导体。探索锂周围的局部结构、其在传导过程中的动态变化以及它们作为全固态电池固体电解质的潜力，是未来研究的重要领域！