ORIGINAL PAPER Lithium-sulfur battery cathodes made of porous biochar support CoFe@NC metal nanoparticles derived from Prussian blue analogues Shengyu Jing 1,2 & Ping Ding 1 & Yongliang Zhang 1 & Huagen Liang 3,4 & Shibin Yin 5 & Panagiotis Tsiakaras 2,6,7 Received: 24 February 2019 /Revised: 11 May 2019 /Accepted: 14 May 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Li–S batteries are considered as candidates for the next-generation secondary batteries due to their high energy density (~ 1672 mAh g -1 ). However, poor conductivity and shuttle effect have become the major obstacles for their development. In the present investigation, we prepared porous biochar-coated metal nanoparticles CoFe@NC/PPC by loading the Prussian blue analogues onto the biomass pomelo peel (PP), followed by calcination. Both rich nitrogen-doped pore structure and CoFe nanoparticles can reduce the shuttle effect in the cycle, and biochar can enhance the conductivity of the sulfur cathode, promoting the complete reaction of sulfur. It is found that after being sulfur-injected and made into a button cell, it exhibits good electro- chemical performance. The initial specific capacity was found to be close to 915.6 mAh g -1 at 1 C and it remained at 447.4 mAh g -1 after 500 cycles with a coulombic efficiency of 97.3%. Keywords Li–S battery . CoFe alloy . Prussian blue analogues . Biomass-derived carbon . Sulfur cathode Introduction Due to excessive energy consumption and the need for more efficient batteries, Li–S batteries have become research hotspots recently [1, 2]. It is expected to become the next generation of secondary batteries because of the advantage of large reserves, high theoretical-specific capacity, low cost and environmental friendliness [3–6]. However, in its devel- opment to commercial use, Li–S batteries were restricted by the following problems: (1) poor conductivity, the conductiv- ity of sulfur is 5 × 10 -30 S/cm at 25 °C, resulting in an incom- plete reaction of the active material [7]; (2) shuttle effect, as intermediate product, polysulfides can dissolve in the electro- lyte and shuttle back and forth between the positive and the negative electrode for parasitic reaction, resulting in a loss of active material [8, 9]; and (3) volume expansion, due to the difference in density, when sulfur is completely reacted to form Li 2 S, there will be theoretically a volume expansion of about 80%, which can lead to the destruction of internal struc- tures [10]. In order to solve the above problems, various materials have been tested and among the preparation methods, the most promising one uses porous carbon as the host of S [11–14]. It has excellent electrical conductivity to promote * Huagen Liang lhg654@gmail.com * Panagiotis Tsiakaras tsiak@uth.gr 1 School of Information and Control Engineering, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China 2 Department of Mechanical Engineering, School of Engineering, University of Thessaly, Pedion Areos, 38834 Volos, Greece 3 Low Carbon Energy Institute, School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China 4 Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China 5 Guangxi Key Laboratory for Electrochemical Energy Materials, Collaborative Innovation Center of Renewable Energy Materials (CICREM), State Key Laboratory of Processing Non-ferrous Metal and Featured Materials, Guangxi University, Nanning 530004, China 6 Institute of High Temperature Electrochemistry, RAS, Yekaterinburg, Russia 620990 7 Ural Federal University, 19 Mira Str., Yekaterinburg, Russia 620002 Ionics https://doi.org/10.1007/s11581-019-03065-7