Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi Boron and phosphorous co-doped porous carbon as high-performance anode for sodium-ion battery Nazir Ahmad 1 , Majid Khan 1 , Xiangjun Zheng, Zhihui Sun, Jin Yan, Chaohui Wei ⁎ , Liwei Shen, Nadia Batool, Ruizhi Yang ⁎ College of Energy, Soochow Institute for Energy and Materials Innovations, Soochow University, Suzhou 215006, China ARTICLE INFO Keywords: Carbon Co-doping Sodium-ion battery Anode ABSTRACT Sodium-ion batteries (SIBs) have attracted extensive attention as the important replacement for lithium-ion batteries, due to the nature abundance of sodium sources. The key to high-performance SIBs lies in appropriate anode material with sufcient space and sites for the difusion and adsorption of sodium ion (Na + ). Heteroatom doping in carbon has proven to be an efective strategy to improve the electrochemical performance of carbon- based anodes for SIB. The feasible preparation of doped carbon is essential for the development of SIBs. Here, boron (B) and phosphorous (P) co-doped honeycomb-like carbon (BPC) has been synthesized by one-step pyr- olysis of onium salts containing B and P. Benefting from dual doping of B and P in carbon, the increased layer space, defects and electrical conductivity of BPC enhance the adsorption capability of Na + , mass transport and charge difusion. The formed porous structure in BPC can promote the electrolyte penetration as well as bufer the volume changes during cycling. When employed as the anode material for SIBs, high storage capacity and excellent cycle life have been enabled. This contribution paves a feasible and controlled approach to prepared heteratom-doped carbons for Na + storage. 1. Introduction • With the fast-growing demand of energy storage for renewable sources and power grids, the conventional lithium-ion batteries (LIBs) can hardly meet such desire, as the limited availability and consequently increasing cost of lithium source. Hence, sodium-ion batteries (SIBs) are broadly regarded as one of the most promising alternatives for lithium-ion batteries (LIBs), due to the natural abundance and environmental-friendliness of the sodium resource, [1–5]. The LIBs and SIBs share similar battery constitution and charge storage mechanism, especially regarding to the cathode. However, the transition from LIBs to SIBs have always been rough [6]. Sodium has greater atom mass (Na: 23 g mol −1 ; Li: 6.9 g mol −1 ), and higher standard electrode potential (Na: −2.71 V vs. SHE; Li: −3.04 V vs. SHE), as compared to those of lithium. Also, the larger radius of Na + (1.02 Å), compared to Li + (0.76 Å), retards the ion difusion rate and induces the sluggish kinetic process of SIBs during the charging/discharging process. These issues could further cause the low capacity and poor cycling performance of SIBs [7,8]. Hence, tremendous eforts have been devoted to exploring suitable anode materials with high Na + storage capacity and rapid reaction dynamics to target high performance SIBs. The current pool of the anode materials for SIBs include carbonaceous material, metal oxide/sulfdes and transition metal dichalcogenides [9,10]. Among them, carbon-based anode material, like graphene, carbon spheres, carbon skeletons, and hard carbon, have been frstly investigated as the anodes of SIBs, due to the good conductivity, low cost and re- source wealth [6,7,11,12] Unfortunately, most carbonaceous ma- terials deliver defcient Na + storage capacity, particularly at the high current density. Accordingly, dopant and structure engineering are regarded as efective strategies to overcome those obstacles. The dopant engineering, involved with the incorporation of single heteroatom like B, N, P, and S to carbon material, can tune the surface chemistry and tailor the structure of the carbon host. These dopants tend to improve electrical conductivity, layer distance, hence accel- erating the charge transport as well as providing additional binding sites for Na + adsorption. Hence, heteroatom doping of carbons have been popularized to achieve SIBs with improved performance. Specifcally, the N atom exhibits higher electronegativity than C atom, https://doi.org/10.1016/j.ssi.2020.115455 Received 16 June 2020; Received in revised form 24 August 2020; Accepted 10 September 2020 ⁎ Corresponding authors. E-mail addresses: chwei@suda.edu.cn (C. Wei), yangrz@suda.edu.cn (R. Yang). 1 These two authors contributed equally to this work. Solid State Ionics 356 (2020) 115455 0167-2738/ © 2020 Published by Elsevier B.V. T