Wang Qinchao of Yangzhou University Nano Energy: High-entropy O3 cathode imparts low-temperature performance to sodium-ion batteries
【Article Information】
The high-entropy O3 cathode imparts low-temperature performance to sodium-ion batteries
Aierxiding Abulikemu
Contact: Yoshiharu Uchimoto*, Han Jie*, Wang Qinchao*
Affiliation: Yangzhou University, Kyoto University
【Background】
Energy storage systems are essential for harnessing renewable energy and reducing carbon emissions. Sodium-ion batteries (SIBs) are seen as an important alternative to lithium-ion batteries (LIBs) in large-scale energy storage due to their low cost and abundant resources, especially in solar/wind power generation and smart grids. However, due to the larger size and weight of Na+, the energy density is low and the kinetic speed is slow, and its practical application is challenging. This research aims to develop cathode materials for sodium-ion batteries with excellent performance to provide high performance and enhanced cycle durability. Recent studies have shown a growing interest in high-entropy oxide (HEO) cathodes. High-entropy cathode materials have unique topology and excellent electrochemical properties. Normally, the disordered arrangement of the TMO6 octahedron stabilizes the lattice in the form of a solid solution through the "entropy stabilization effect". The "entropy stabilization effect" can delay and alleviate complex phase transitions, and achieve highly reversible phase transitions from O3 to P3, resulting in excellent cycling performance and fast cycling capabilities, and is expected to achieve high capacity and extended cycle life in low temperature environments.
【Introduction】
Recently, Dr. Wang Qinchao and Professor Han Jie of Yangzhou University and Professor Yoshiharu Uchimoto of Kyoto University published an article entitled "High-Entropy O3-Type Cathode Enabling Low-Temperature Performance for Sodium-Ion Batteries" in the internationally renowned journal Nano Energy. In this work, they focused on how to rationally design HEO cathode materials to achieve excellent sodium intercalation/expulsion performance. The design and synthesis of HEO O3 type cathodes revolves around two key criteria: high capacity and high stability. Enhancing the redox reaction of active transition metals is essential to increase capacity, which is determined by their theoretical density of states (DOS) electron levels. On the other hand, improving the stability of the O3 structure during cycling requires fine-tuning of the chemical environment of the TMO6 octahedron.
Reducing the difference in cation size to less than 15% can promote the disordered arrangement of TMO6 octahedral. Guided by these two standards, they synthesized a series of HEO O3 cathode materials, among which O3-Na[FeCoNiTi]1/6Mn1/4Zn1/12O2 (FCNTMZ1/12) exhibited the most excellent electrochemical performance, and it is worth noting that the synthesized FCNTMZ1/12 cathode exhibited excellent low-temperature performance, providing capacities of 109.6 mAh g-1 and 91.1 mAh g-1 at 0.1C and 1C, respectively. This work proposes a novel strategy for the design and synthesis of HEO cathodes, providing valuable insights for the realization of high-performance sodium-ion batteries.
【Main points of the text】
Point 1: Design of high-entropy O3 cathode materials
High-entropy O3 cathode materials are composed of five or more metallic elements in almost equal proportions and are of great interest due to their unique energy storage properties. When designing and synthesizing HEO O3 type cathodes, two key criteria must be taken into account: high capacity and highly stable structure. In order to obtain high reversible capacities, the energy level selection of the redox pairs of active transition metals (TMs) is the key to match the sodium storage voltage window. Using the experimental voltage curve distribution and DOS, a schematic diagram of the energy level of TMs was constructed. Within the same layered structure framework, the electronic energy level order of TMs is: Mn4+/3+ > Ni3+/2+ > Ni4+/3+ >Fe4+/3+> Co4+/3+. In addition, the cation size difference should be less than 15% relative to active TMs.
Transition metal ions in the shaded region are usually selected to regulate the chemical environment of the TMO6 octahedron, resulting in a disordered arrangement within the TMO2 layer. In addition, Mn3+ exhibits a strong Jahn-Teller effect, resulting in lattice distortion and repeated cyclic degradation. The addition of inactive and low-valent metals, such as Zn2+, Li+, and Mg2+, helps stabilize the Mn4+ state. Different elements in the HEO cathode enhance the "entropy stabilization effect". At the same time, the doping of inert Ti4+ and Zn2+ further refines the local electronic structure. Based on the above criteria, the synthesized Na[FeCoNiTi]1/6Mn1/4Zn1/12O2 (FCNTMZ) cathode exhibits excellent sodium storage performance, which is worthy of further study.
Figure 1. HEO cathode design guidelines
要点二：HEO O3 FCNTMZ正极储钠性能
At 25 °C, the reversible specific capacity of the FCNTMZ1/12 cathode is 127.3 m Ah g-1 and the first coulombic efficiency is about 83.0 %. At -20 °C, the FCNTMZ1/12 positive electrode still provides a capacity of 109.6 mAh g-1 at 0.1 °C, which is about 86.1% of its capacity at 25 °C. The FCNTMZ1/12 cathode retains 80% and 92% of its capacity after 100 cycles at 0.1C at 25 °C and -20 °C, respectively. Even at a high current rate of 5C, the FCNTMZ1/12 cathode retains its capacity at 69% after 1000 cycles at 25 °C. At -20 °C, 90.2% and 87.8% of the initial capacity were maintained after 600 and 1000 cycles at 1C, respectively, indicating that it had excellent stability at low temperatures.
Figure 2. Sodium storage performance of HEO O3 FCNTMZ cathode
Point 3: Structural evolution of HEO O3 FCNTMZ cathode charging and discharging process
To study the structure evolution in detail, in-situ XRD experiments were performed at 0.1C magnification. The (003) and (006) peaks of the O3 phase shift to a lower angle during charging, and the intensity of the O3 phase decreases, with a new peak at 15.8°, indicating the appearance of the P3 phase. At 3.6 V, the initial O3 phase diffraction peak disappeared completely, and the P3 phase dominated. In the first discharge, the structural evolution is reversed from the first charge. The return of lattice parameters A(b) and C to the initial state indicates that the FCNTMZ1/12 structural transition is highly reversible. On the second charge, the structural changes are exactly the same as those observed on the first charge. The reversibility of the deterioration structure of O3', O3" and P'3 phases is not involved in the whole charge-discharge process, which affects the cycling stability. The change in unit cell volume before and after sodium ion intercalation/expulsion is only 3%, ensuring excellent electrochemical performance.
Figure 3. Evolution of the cathode structure of FCNTMZ.
要点四：HEO O3 FCNTMZ正极电荷补偿机理
To study the charge compensation of the active elements in the FCNTMZ1/12 cathode, ex situ XAS measurements were made in the original state, fully charged (4.1 V), and fully discharged (2.0 V), respectively. The total reversible capacity of the Ni2+/Ni4+, Fe3+/Fe3.6+, and Co3+/CO3.6+ redox pairs is 127 mAh g-1 during the first charge/discharge. At this time, the length of the TM-O1 and TM-O2 bonds in the P3 structure is reduced by about 2.5-9.9 % and 0.5-5.4 %, respectively. At the same time, the TM-TM distance is reduced by about 0.3 - 2.1 %. Compared with the TM-O2 distance, the decrease of the TM-O1 distance is more significant, indicating that the O1 in the P3 structure causes a strong stress change. In addition, even inactive Mn4+ shrinks in the Mn-O and Mn-TM bonds, suggesting that it is involved in the rearrangement of the overall structure. After discharging to 2.0 V, the P3 structure reverts to the O3 structure and the distance between the TM-O and TM-TM bonds returns to their original length. This is consistent with the reversible structural transitions and small volume changes observed with in-situ XRD. The size difference of the selected cations is less than 15 %, which can easily lead to the reduction of the bond length change of TM-O and TM-TM, thereby enhancing the structural stability in the short-range local environment.
Figure 4. FCNTMZ positive electrode charge compensation mechanism
Point 5: HEO O3 FCNTMZ cathode whole battery and kinetic performance
The kinetic properties of the FCNTMZ1/12 cathode material were characterized by measuring the diffusion coefficient of Na+ by cyclic voltammetry and galvanostatic batch titration at 25 °C and -20 °C. The calculated DNa+ value decreased from 10-11 cm2 s-1 at 25 °C to 10-12 cm2 s-1 at -20 °C. The high-entropy structure of the NFCMTZ1/12 cathode not only maintains the stability of the O3 phase, but also minimizes the O3-P3 structure transition during Na+ ejection/embedding, thus promoting more efficient Na+ transport. In order to further explore its application prospects, a whole battery was constructed with FCNTMZ1/12 as the positive electrode and hard carbon as the negative electrode. At a current density of 30 mA g-1, the full battery provides a capacity of about 112 mAh g-1, retaining 79% of its initial discharge capacity after 50 cycles. These excellent electrochemical properties further validate the potential of O3-FCNTMZ1/12 as a cathode material for sodium-ion batteries.
Figure 5: HEO O3 FCNTMZ cathode whole cell and kinetic performance
Summary and outlook
In summary, two key criteria for HEO O3 cathode design and synthesis were identified: high performance and stable cathode structure. Increasing the amount of active TMs with electron energy levels within the electrochemical window can increase the capacity. At the same time, keeping the cation size difference below 15% can ensure the stability of the structure. They synthesized a variety of HEO O3 phase cathode materials. Among them, the O3-FCNTMZ1/12 cathode material exhibits a reversible capacity of 127.3 mAh g-1 at 0.1 C, with excellent long-cycle stability (69 % after 1000 cycles at 5C) and excellent rate performance.
Due to its HEO configuration, the O3-FCNTMZ1/12 cathode exhibits excellent performance at low temperatures. At -20 °C, it maintains a stable 91.1 mAh g-1 reversible capacity at 1C, retaining about 88% of the capacity after 1000 cycles. In addition, DNa+ decreased only from 14.4 × 10-12 cm2 s-1 at 25 °C to 3.06 × 10-12 cm2 s-1 at -20 °C. In-situ XRD measurements confirmed that FCNTMZ1/12 underwent a reversible structural transition from O3 to P3 with a volume change of less than 3%. The in-situ XAS results show that the charge compensation is provided by Ni2+/Ni4+, Fe3+/Fe3.6+, and Co3+/Co3.6+. In addition, the TM-O distance shrinkage was less than 9.9 %, and the TM-TM distance shrinkage was 2.1%, which effectively inhibited the structural rearrangement and alleviated the volume expansion. These standards provide a strategic approach for the design and development of HEO cathodes for high-performance sodium-ion batteries, especially for cryogenic applications.
【Article Link】
High-Entropy O3-Type Cathode Enabling Low-Temperature Performance for Sodium-Ion Batteries
https://www.sciencedirect.com/science/article/pii/S2211285524005615?via%3Dihub#fig0010
【About the Corresponding Author】
Dr. Wang Qinchao graduated from the Department of Materials Science of Fudan University in 2018 with a Ph.D. in Materials Physics and Chemistry, and continued to engage in postdoctoral research at Fudan University, and visited Brookhaven National Laboratory in the United States in 2019. In 2021, he returned to China and was introduced to the School of Chemistry and Chemical Engineering of Yangzhou University as a distinguished professor of the school. In 2022, he was awarded the Doctor of Entrepreneurship and Entrepreneurship in Jiangsu Province, and in 2023, he was the vice president of science and technology in Jiangsu Province. He is mainly engaged in the research of cathode materials and solid-state electrolytes for lithium-ion batteries and sodium-ion batteries, and the physical and chemical problems of cathode materials for secondary batteries by synchrotron radiation technology. He presided over the completion of the National Natural Science Foundation of China Youth Project, and the China Postdoctoral Fund. As the first author or corresponding author in J. J. Am. Chem. Soc.，Nat. He has published a number of papers in journals such as Commun., Adv. Energy Mater., Adv. Sci., Nano Energy, etc., and has been authorized 3 Chinese invention patents.
Professor Han Jie, doctoral supervisor, winner of the National Excellent Youth Award, Vice President of Yangzhou University. In 2008, he graduated from the School of Chemistry and Chemical Engineering of Yangzhou University with a doctorate degree in science. In 2012, he was a visiting scholar at the University of California, Riverside. He has long been engaged in the assembly and catalysis of conductive polymer functional materials, the synthesis, assembly and application of stimulus-responsive functional amphiphilic molecules, and the structural design, synthesis and application of functional composite catalysts. He has presided over 4 projects of the National Natural Science Foundation of China. Am. Chem. Soc.、Adv. Mater. 、Prog. Polym. He has published more than 100 papers in journals such as Sci. and Chem. Commun.
In 2010, he was nominated for the National 100 Outstanding Doctoral Dissertation Award, in 2012, he won the second prize of Natural Science Award of the Ministry of Education (ranked second), and in 2013, he won the first prize of the first "Oriental Gelatinization" Cup National Colloid and Interface Outstanding Young Teacher in Chemistry. In 2016, he was awarded the training object of young and middle-aged academic leaders in the "Blue Project" of colleges and universities in Jiangsu Province, and in 2017, he was selected into the 14th batch of "Six Talent Peaks" high-level talent plan in Jiangsu Province, and in the same year, he was awarded the title of young and middle-aged experts with outstanding contributions in Yangzhou City, and in 2020, he won the 3rd Jiangsu Chemistry and Chemical Engineering Society-Dai Anbang Youth Innovation Award.
【Group Introduction】
The Electrochemical Energy Storage Research Group at Yangzhou University is led by Prof. Jie Han and includes Dr. Qinchao Wang, Dr. Chao Wang, Dr. Pan Xue, and Dr. Xiaoge Li. The electrochemical energy storage research group of Yangzhou University is committed to the research of new energy energy storage materials and devices and related basic scientific issues, mainly including the development and research of electrode materials for lithium-ion batteries and sodium-ion batteries, the energy storage mechanism of electrode materials by lithium-ion solid-state electrolyte and synchrotron radiation X-ray technology, and the development of in-situ optical microscopy and fluorescence technology. Our group will further promote and strengthen the development and research of new energy energy storage materials and devices, and promote the development of new energy energy storage.