Sustainable Energy Storage: Recent Trends and Developments toward Fully Organic Batteries

Abstract

In times of spreading mobile devices, organic batteries represent a promising approach to replace the well-established lithium-ion technology to fulfill the growing demand for small, flexible, safe, as well as sustainable energy storage solutions. In the last years, large efforts have been made regarding the investigation and development of batteries that use organic active materials since they feature superior properties compared to metal-based, in particular lithium-based, energy-storage systems in terms of flexibility and safety as well as with regard to resource availability and disposal. This Review compiles an overview over the most recent studies on the topic. It focuses on the different types of applied active materials, covering both known systems that are optimized and novel structures that aim at being established.

Keywords: electrochemistry; energy storage; hybrid metal-organic batteries; organic batteries; redox chemistry.

Figure 1

Predicted demands (left), production, and reserves (right) of lithium and cobalt resources for the battery industry (reprinted by permission from Springer Nature, Copyright 2018).2

Scheme 1

Discharging and charging process of an electrochemical cell (adapted with permission from Springer Nature, Copyright 2017).13

Scheme 2

Top: Molecular structures and theoretical specific capacities of common quinones. Bottom: General redox mechanism of quinones.

Figure 2

Long‐term performance of a hybrid lithium‐ion cell based on Lawsone (shown as a greenish powder in the right inset) as active material, revealing a discharge capacity that remains stable over 1000 consecutive cycles (reprinted with permission from Wiley, Copyright 2017).34

Figure 3

Left: Molecular structures of a TCAQ‐containing polymethacrylamide and poly(2‐vinylthianthrene), which constitute the active materials of a fully organic cell. Right: Respective charge/discharge curves at 1 C and 5 C, showing a capacity fade of 30 % over 250 cycles. (Reprinted with permission from Wiley, Copyright 2017).43

Figure 4

Left: Molecular structure of pyrene‐4,5,9,10‐tetraone. Right: Performance of a respective cell with a PbO₂ counter electrode. The capacity remained nearly stable over 1500 consecutive charge/discharge cycles, while the voltage–capacity curves show a capacity loss of only 20 % by changing from a charge/discharge rate of 0.1 C to 20 C. (Reprinted with permission from Springer Nature, Copyright 2017).47

Figure 5

Left: Molecular structure of the anthra‐ and benzoquinone‐containing COFs (TFP=1,3,5‐tris(4‐formylphenyl)benzene). Right: Respective cycling data showing the high and stable capacity received for the exfoliated COF (ECOF) containing anthraquinone units (DAAQ‐ECOF) compared to the non‐exfoliated material (DAAQ‐TFP‐COF, with a likewise stable but lower capacity) and the unstable free 2,6‐diaminoanthraquinone (DAAQ). (Reprinted with permission from the American Chemical Society, Copyright 2017).50a

Figure 6

Performance of a PAQS‐Ni(OH)₂ cell. Top left: Potential profiles of both electrodes during charging and discharging, compared to a metal–hydride electrode (MmH), showing stable, single plateaus. Top right: Course of the charge/discharge capacity over 1300 cycles with a loss of ca. 10 %. Bottom left: Exchange current density and charge‐transfer resistance of the polymer electrode and a metal–hydride electrode (MnH) within a temperature range of −40 to 30 °C, demonstrating the improved temperature independence of the polymer electrode. Bottom right: Specific capacity of the cell at different charge/discharge currents and temperatures, revealing only small losses of the capacity at higher currents and lower temperature. (Reprinted with permission from Springer Nature, Copyright 2017).47

Scheme 3

Modification of MWCNTs with anthraquinone (reprinted with permission of the Royal Society of Chemistry, Copyright 2016).53

Figure 7

Top: Working principle of a poly(EDOT‐quinone)‐containing fully organic cell based on proton exchange via a pyridine electrolyte. Bottom: Related electrochemical characteristics, in particular the cyclovoltammograms of the active materials poly(EDOT‐anthraquinone) and poly(EDOT‐benzoquinone) (left), the charge/discharge voltage curve of a respective cell (middle), and a differential capacity plot derived from the latter data resembling the voltammetry experiment (right). (Reprinted with permission from the American Chemical Society, Copyright 2017).62

Scheme 4

Top: Molecular structures of common aromatic diimides with theoretical specific capacities. Bottom: General redox mechanism of aromatic diimides.

Figure 8

Left: Schematic representation of the active polymer materials of all‐organic poly(diimide)/poly(triphenylamine) cells. Right: Performance characteristics of a poly(NDI)/poly(triphenylamine) cell, revealing sloping charge/discharge voltages (top) but relatively stable capacities over 700 cycles (bottom). (Reprinted with permission from Wiley, Copyright 2017).74

Figure 9

Performance of a poly(perylene diimide)/poly(triphenylamine) cell, in particular voltage profiles (top left) and capacities at different charge/discharge currents (top right), revealing a good rate capability of the system, as well as the capacity development over 2000 cycles (bottom), showing a good long‐term stability. (Reprinted with permission of the Royal Society of Chemistry, Copyright 2018).74, 75

Figure 10

Left: Molecular structure of a norbornene‐NDI polymer used as active material in a hybrid lithium‐ion cell. Middle: Voltage profiles of the 1^st, 250^th, and 500^th charge/discharge cycles of the cell, revealing a stable performance. Right: Voltage profiles at different charge/discharge currents, demonstrating the good rate capability of the system. (Reprinted with permission the Materials Research Society, Copyright 2017).79a

Figure 11

Characteristics of a fiber‐shaped hybrid lithium‐ion cell based on poly(NDI) on CNTs. Top left: Voltage curves at different charge/discharge rates demonstrating a good rate capability. Top right: Comparison of the performance of the cell with other systems via a Ragone plot. Bottom: Depiction of the charge/discharge capacity over 1500 cycles and several currents, showing a good long‐term stability and rate capability. (Reprinted with permission from the Royal Society of Chemistry, Copyright 2016).83d

Scheme 5

General redox mechanism of terephthalates.

Figure 12

Top: Schematic representation of the mechanism of the two redox processes used for a symmetric all‐organic cell based on terephthalate active material and Li⁺‐containing electrolyte. Bottom left: Voltage profiles of the first four charge/discharge cycles of the cell. Bottom right: Capacity development of the cell over 300 cycles with a moderate loss of 20 %. (Reproduced under Creative Commons License, http://creativecommons.org/licenses/by/4.0/).90

Figure 13

Top: SEM images of calcium terephthalate silver composites, showing a decreasing particle size and increasing particle uniformity with increasing silver precursor content. Bottom: Performance characteristics of respective hybrid lithium cells, in particular the charge/discharge capacity over 130 consecutive cycles and voltage profiles at different currents and silver precursor contents, demonstrating an optimum of the latter at 5 wt %. (Reprinted with permission from the Royal Society of Chemistry, Copyright 2016).96

Figure 14

Top: Working principle of an all‐organic cell based on perylene‐tetracarboxylate and a poly(perylene‐diimide) as active materials and a Li⁺‐containing electrolyte. Bottom left: Capacity development of the cell over 200 charge/discharge cycles, revealing a drop of 20 % within the first 50 cycles followed by a stable performance over 150 cycles. Bottom right: Voltage curves of the first five cycles. (Reprinted with permission from the American Chemical Society, Copyright 2017).76

Scheme 6

Top: Molecular structures of organic radical moieties and their preferential redox reactions. Bottom: Organic radicals recently used in organic cells.

Figure 15

Top: SEM image of single‐walled CNTs prepared by means of eDIPS. Bottom: Performance characteristics of an all‐organic beaker‐type cell containing an anthraquinone‐based anode and a cathode from poly(TEMPO acrylamide) and single‐walled CNTs, in particular the voltage profiles at different charge/discharge currents (left) and the course of the capacity over 1000 consecutive cycles, revealing a loss of 30 % (right). (Reprinted with permission from Wiley, Copyright 2018).113

Figure 16

An electrode based on cross‐linked TEMPO gel polymer. Top left: SEM image of the electrode consisting of agglomerated particles. Top right: Photograph of the bent electrode. Bottom left: Voltage curves for the charging/discharging of a respective hybrid lithium‐ion cell at different currents. Bottom right: Capacity development over 500 cycles in comparison to a cell containing the non‐cross‐linked counterpart. (Reprinted with permission of the Electrochemical Society, Copyright 2017).118

Figure 17

Molecular structures of conjugated polymers that were tested in organic batteries.

Figure 18

Two‐dimensional polytriphenylamine networks in hybrid lithium cells. Top left: Molecular structure. Top right: Capacity development at different charge/discharge currents and over 1600 cycles for both systems (black and red), demonstrating both good rate capabilities and long‐term stabilities. Middle: SEM images of the obtained microporous structures with different specific surface areas, showing aggregates of 60–80 nm in both cases. Bottom: Charge/discharge curves of the respective hybrid lithium cells at different currents. (Reprinted with permission from Elsevier, Copyright 2016).131

Figure 19

Heterocyclic moieties and other aromatic compounds that were tested as active materials for organic batteries.