Enhancing reversible Na-ion intercalation by introducing K-ions into layered vanadyl phosphate for sodium-ion battery cathodes
Runzhe Wei,
Yi Lu,
Wanjun Ren,
Yupei Han,
Ajay Piriya Vijaya Kumar Saroja,
Xueming Xia,
Pan He,
Charlie A F Nason,
Zhixin Sun,
Jawwad A Darr,
Jiayan Luo,
Min Zhou,
Yang Xu
Affiliations
Runzhe Wei
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Yi Lu
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Wanjun Ren
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Yupei Han
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Ajay Piriya Vijaya Kumar Saroja
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Xueming Xia
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Pan He
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Charlie A F Nason
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Zhixin Sun
Hefei National Research Centre for Physical Sciences at the Microscale, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, People’s Republic of China
Jawwad A Darr
Department of Chemistry, University College London , London WC1H 0AJ, United Kingdom
Jiayan Luo
State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University , Shanghai 200240, People’s Republic of China
Hefei National Research Centre for Physical Sciences at the Microscale, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, People’s Republic of China
Vanadium-based phosphates are being extensively studied as an important family of sodium-ion battery (SIB) cathodes. Among many compositions, NaVOPO _4 is considered because of various polymorphs and the high redox potential of V ^4+/5+ . However, due to relatively poor intrinsic kinetics and electronic conductivity, approaches such as nanostructuring and carbon composites are commonly used to avoid fast performance degradation. Being different from mainstream approaches, this work utilizes the knowledge gained from potassium-ion batteries (PIBs) and applies layered KVOPO _4 , a PIB cathode material, as a SIB cathode material. The results demonstrate that KVOPO _4 experiences an electrochemical K ^+ -Na ^+ exchange during the initial cycle and a Na-dominated (de)intercalation process in the following cycles. The initial exchange results in a small amount of K ^+ (∼0.1 K per formula) remaining in the interlayer space and owing to the larger size of K ^+ than Na ^+ , the residual K ^+ effectively acts as ‘pillars’ to expand interlayer spacing and facilitates the Na (de)intercalation, leading to enhanced reversible Na storage and diffusion kinetics of KVOPO _4 compared to its Na counterpart NaVOPO _4 . KVOPO _4 delivers an initial discharge capacity of 120 mAh g ^−1 (90% of the theoretical capacity) at 10 mA g ^−1 and retains 88% capacity after 150 cycles. It also delivers 52 mAh g ^−1 at 1 A g ^−1 and 91% capacity retention after 1000 cycles at 100 mA g ^−1 , completely outperforming NaVOPO _4 .
