Dual Metal-Ion Preintercalation of Bilayered Vanadium Oxide Cathode Enables Synergistically Enhanced Intercalation Battery Performance

In this work, we demonstrate a synthesis strategy for enhancing the performance of intercalation battery electrodes via chemical preintercalation of two types of metal ions. We will illustrate the developed strategy by presenting bilayered vanadium oxide (BVO) simultaneously preintercalated with Li⁺ and Mg²⁺ ions and showcase the synergistically enhanced capacity and cycling stability using the lithium-ion battery system as an example. We found that the Li⁺ and Mg²⁺ ions can be preintercalated into an interlayer region of BVO structure separately through a two-step approach. The first step introduces Mg²⁺ ions using a wet-chemical precipitation step. In the second step, Li⁺ ions were preintercalated by hydrothermal treatment of the precipitate in LiCl solution. We determined and compared the number of preintercalated Mg²⁺ ions before and after hydrothermal treatment using atomic absorption spectroscopy (AAS) and concluded that the Li⁺ ions were preintercalated by partial exchange with Mg²⁺ ions in the second step. The Li⁺ ion storage properties of the Li⁺ & Mg²⁺ simultaneously preintercalated phase (LMVO) were investigated with the reference of Li-preintercalated BVO (LVO) and Mg-preintercalated BVO (MVO). LMVO electrode exhibited 2^nd cycle specific capacity of 245 mAh g^-1, which is comparable to 280 mAh g^-1delivered by LVO and is significantly higher than 175 mAh g^-1 delivered by MVO. After 50 cycles, the LMVO retained 58% of its 2^nd cycle capacity, which is comparable to the 67% capacity retention of MVO and significantly higher than the 22% capacity retention of LVO. Therefore, our study for the first time experimentally confirms the hypothesis ^{1, 2} that chemical preintercalation of electrochemically active ions facilitates solid-state ion diffusion, thus leading to increased specific capacity; and chemical preintercalation of electrochemically inactive ions stabilizes the structure of electrode materials, thus improving the cycling stability. Additionally, the role of structural water in the LMVO phase on its electrochemical cycling performance was investigated. By employing low temperature annealing ³ for both active material and electrodes, the cycling stability of LMVO after 50 cycles can be further improved by 21% due to reduced amount of structural water. The low temperature annealed LMVO retained 174 mAh g^-1 after 50 cycles at a current density of 20 mA g^-1, and able to deliver 153 mAh g^-1 at a current density of 200 mA g^-1. Our findings shed light on the role of structural water and diverse chemically preintercalated ions in the interlayer regions of layered electrode materials, providing insights into developing novel electrode materials with enhanced electrochemical properties for next-generation energy storage systems beyond lithium-ion batteries.<br/><br/><b>References</b><br/>(1) Pomerantseva, E. Chemical Preintercalation Synthesis of Versatile Electrode Materials for Electrochemical Energy Storage. <i>Accounts of Chemical Research </i><b>2022</b>.<br/>(2) Clites, M.; Pomerantseva, E. Bilayered vanadium oxides by chemical pre-intercalation of alkali and alkali-earth ions as battery electrodes. <i>Energy Storage Materials </i><b>2018</b>, <i>11</i>, 30-37.<br/>(3) Clites, M.; Hart, J. L.; Taheri, M. L.; Pomerantseva, E. Annealing-Assisted Enhancement of Electrochemical Stability of Na-Preintercalated Bilayered Vanadium Oxide Electrodes in Na-Ion Batteries. <i>ACS Applied Energy Materials </i><b>2020</b>, <i>3</i> (1), 1063-1075.