A Scalable Approach to Na₂FeP₂O₇@Carbon/Expanded Graphite as a Low‐Cost and High‐Performance Cathode for Sodium‐Ion Batteries

Abstract

Sodium-ion batteries (SIBs) are the most promising candidates as alternatives to lithium-ion batteries (LIBs), owing to the natural abundance of sodium salt and the low cost. However, the commercial application of SIBs is principally hampered by the absence of suitable cathode materials. Herein, a novel Na 2 FeP 2 O 7 @carbon/expanded graphite (NFPO@C/EG) composite with a unique microstructure was developed through a scalable sol-gel process followed by a ball-milling procedure with expanded graphite. Benefiting from the multiscale carbonmodified structure, the NFPO@C/EG effectively improves the electronic conductivity and, at the same time, shortens the path of sodium ion transmission. As a consequence, the NFPO@C/EG cathode presents a much higher specific capacity and more stable cycling stability than NFPO@C and NFPO. The unique design of NFPO@C/EG endows a high ratio of pseudocapacitance contribution and a large Na + diffusion coefficient. As a consequence, the NFPO@C/EG cathode displays stable cycle performance (82 mAh g À 1 over 400 cycles at 232 mA g À 1) and superior rate capability (60 mAh g À 1 at a high charge/discharge density of 2320 mA g À 1). This multiscale carbon-modified design concept builds an avenue for the practical application of polyanionic cathode materials and promotes the development of low-cost SIBs.

Iron‐Phosphate‐Based Cathode Materials for Cost‐Effective Sodium‐Ion Batteries: Development, Challenges, and Prospects

“…Reproduced with permission. [ 51 ] Copyright 2020, Wiley‐VCH. g) The long‐term electrochemical performance of pristine Na 2 FeP 2 O 7 and Mg‐doped Na 2 FeP 2 O 7 materials.…”

“…In another study, an unique pyrolytic carbon layer and expanded graphite (EG) conductive framework were designed through a sol‐gel method companied with ball‐milling, as shown in Figure 8e. [ 51 ] With enhanced reaction kinetics, the Na 2 FeP 2 O 7 @C/EG showed considerable reversible capacity and flat voltage platforms (Figure 8f). Cycling stability and rate performance of the Na 2 FeP 2 O 7 @C/EG are also excellent, with 82 mA h g −1 of specific capacity at the current density of 232 mA g −1 after 400 cycles, and 60 mA h g −1 can still be obtained when the current density is increased to 2320 mA g –1 .…”

“…e) TEM image and f) charge-discharge profiles of Na 2 FeP 2 O 7 @C/EG cathode material. Reproduced with permission [51]. Copyright 2020, Wiley-VCH.…”

Three‐Dimensional Holey Graphene Modified Na4Fe3(PO4)2(P2O7)/C as a High‐Performance Cathode for Rechargeable Sodium‐Ion Batteries

“…The earth is rich in Na, Fe and P resources, and the polyanionic phosphate-based cathode materials such as NaFe-PO 4 , Na 2 FeP 2 O 7 , FePO 4 and Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) for SIBs have been investigated. [7][8][9][10][11][12] As olivine NaFePO 4 is not stable and cannot be obtained by conventional preparation methods, it is not suitable for large-scale production. [9] The electrochemical activity of maricite NaFePO 4 greatly depends on its nanoscale size, and it has a low working voltage, which is unbeneficial to commercial applications.…”

Three‐Dimensional Graphene Network Decorated with Highly Symmetrical Cuboid Na3V2(PO4)2F3 Particles: High Rate Capability and Cycling Stability for Sodium‐Ion Batteries

“…Recently, SIB has received extensive attentions because of its rich natural abundance and relatively low cost [1] . Particularly, the cathode material is recognized as one of the core factors that could surmount the limitation of the SIB electrochemical performance as it could improve capacity and voltage [2] . Therefore, it can be considered that probe cathode materials with significantly high energy density and greatly stabilized cycling capability [3]…”