Advances in Organic Anode Materials for Na-/K-Ion Rechargeable Batteries

Abstract

Electrochemical energy storage (EES) devices are gaining ever greater prominence in the quest for global energy security. With increasing applications and widening scope, rechargeable battery technology is gradually finding avenues for more abundant and sustainable systems such as Na-ion (NIB) and K-ion batteries (KIB). Development of suitable electrode materials lies at the core of this transition. Organic redox-active molecules are attractive candidates as negative electrode materials owing to their low redox potentials and the fact that they can be obtained from biomass. Also, the rich structural diversity allows integration into several solid-state polymeric materials. Research in this domain is increasingly focused on deploying molecular engineering to address specific electrochemical limitations that hamper competition with rival materials. This Minireview aims to summarize the advances in both the electrochemical properties and the materials development of organic anode materials.

Keywords: anode; battery; organic electrode; potassium-ion; sodium-ion.

Figure 1

Redox states for organic moieties typically employed as anodes in secondary batteries.

Scheme 1

Illustration showing different aspects of organic anode materials. (CC – current collector, A – anode, S – separator, E – electrolyte, C – cathode).

Scheme 2

Schematic depiction of the progress from identifying redox‐active moiety to material development for further application.

Figure 2

a) Chemical diagram showing molecular reorganization upon Na⁺ insertion. b) Cycling performance of Na₂TP at current rate of 30 mAh g⁻¹. Reproduced with permission.40 Copyright 2012, Wiley.

Figure 3

Flowchart of converting waste PET bottles to usable terephthalate for Na⁺/Li⁺ ion insertions. Reproduced with permission.45 Copyright 2020, American Chemical Society.

Figure 4

a) Chemical diagram showing redox reactions at two different voltages. b) The discharge/charge profile at initial cycles at current rate of 19 mAh g⁻¹. c) Cycling performance over 100 cycles. Reproduced with permission.47 Copyright 2014, Wiley.

Figure 5

Discharge voltages for Na₂TP and derivatives in a) Na cell and b) Li cell. Optimised molecular structures for Na₂(MeO)₂TP upon insertion of c) Li⁺ and d) Na⁺. Reproduced with permission.49 Copyright 2019, Royal Society of Chemistry.

Figure 6

a) Figure showing the layered structure in Na₂SDC (SSDC) for Na⁺ storage. b) Comparison of rate capability with Na₂TP (SBDC). Reproduced with permission.55 Copyright 2015, American Chemical Society.

Figure 7

a) Structure of Na₂NDC. b) High‐temperature PXRD (HT‐PXRD) patterns showing thermal stability. c) Cycling performance at 100 mA g⁻¹ (red) and 400 mA g⁻¹ (blue). Reproduced with permission.59 Copyright 2019, Wiley.

Figure 8

a) Proposed mechanism in CHDA for Na⁺ storage. b) Cyclic voltammetry profile for the first 5 cycles. Reproduced with permission.61 Copyright 2018, Wiley.

Figure 9

a) Molecules with different extent of S‐atom substitution. b) Rate capability for molecules a–d. c) Calculated HOMO energy levels and sites of interaction for Na⁺. Reproduced with permission.63 Copyright 2017, Wiley.

Figure 10

a) Proposed mechanism for Na⁺ insertion and stabilization of the radical. b) EPR profiles are different stages of cycling. c) Cycling performance of TSAQ (tris N‐salicylideneanthraquinoylamine) over 2500 cycles. Reproduced with permission.67 Copyright 2016, Nature Publishing Group.

Figure 11

a) Proposed mechanism for K⁺ storage in perylene based diimide system. b) Structural packing showing presence of stacking interactions. c) Comparison of performance with reported anode materials for KIB. Reproduced with permission.78 Copyright 2019, Royal Society of Chemistry.

Figure 12

a) Proposed mechanism for K⁺ insertion in azo based molecule. b) Cycling performance at high current rate and elevated temperature (60 °C). Reproduced with permission.80 Copyright 2019, Wiley.

Figure 13

a) Packing diagram for Zn−PTC and Na₄−PTC and corresponding Na⁺ ion insertions. b) Solid‐state NMR and c) in‐situ PXRD patterns at different stage of cycling showing activation of unsaturated bonds and structural stability. Reproduced with permission.89 Copyright 2018, Elsevier.

Figure 14

a) Molecular structure of CON‐10 and CON‐16. b) Rate performance for the two compounds relative to RGO (reduced graphene oxide). Reproduced with permission.94 Copyright 2018, American Chemical Society.

Figure 15

Packing diagram of COF‐10 and the predicted interaction of K⁺ with the π‐rich core of the compound. Reproduced with permission.98 Copyright 2019, American Chemical Society.