Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

https://hal.archives-ouvertes.fr/hal-02417326/document

Materials for electrochemical capacitors

In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

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A review of electrode materials for electrochemical supercapacitors

Energy storage using batteries offers a solution to the intermittent nature of energy production from renewable sources; however, such technology must be sustainable. This Review discusses battery development from a sustainability perspective, considering the energy and environmental costs of state-of-the-art Li-ion batteries and the design of new systems beyond Li-ion. Images: batteries, car, globe: © iStock/Thinkstock.

Towards greener and more sustainable batteries for electrical energy storage

Research Development on Sodium-Ion Batteries

The status of ambient temperature sodium ion batteries is reviewed in light of recent developments in anode, electrolyte and cathode materials. These devices, although early in their stage of development, are promising for large-scale grid storage applications due to the abundance and very low cost of sodium-containing precursors used to make the components. The engineering knowledge developed recently for highly successful Li ion batteries can be leveraged to ensure rapid progress in this area, although different electrode materials and electrolytes will be required for dual intercalation systems based on sodium. In particular, new anode materials need to be identified, since the graphite anode, commonly used in lithium systems, does not intercalate sodium to any appreciable extent. A wider array of choices is available for cathodes, including high performance layered transition metal oxides and polyanionic compounds. Recent developments in electrodes are encouraging, but a great deal of research is necessary, particularly in new electrolytes, and the understanding of the SEI films. The engineering modeling calculations of Na-ion battery energy density indicate that 210 Wh kg−1 in gravimetric energy is possible for Na-ion batteries compared to existing Li-ion technology if a cathode capacity of 200 mAh g−1 and a 500 mAh g−1 anode can be discovered with an average cell potential of 3.3 V.

Sodium‐Ion Batteries

Recently, lithium-ion batteries have been attracting more interest for use in automotive applications. Lithium resources are confirmed to be unevenly distributed in South America, and the cost of the lithium raw materials has roughly doubled from the first practical application in 1991 to the present and is increasing due to global demand for lithium-ion accumulators. Since the electrochemical equivalent and standard potential of sodium are the most advantageous after lithium, sodium based energy storage is of great interest to realize lithium-free high energy and high voltage batteries. However, to the best of our knowledge, there have been no successful reports on electrochemical sodium insertion materials for battery applications; the major challenge is the negative electrode and its passivation. In this study, we achieve high capacity and excellent reversibility sodium-insertion performance of hard-carbon and layered NaNi0.5Mn0.5O2 electrodes in propylene carbonate electrolyte solutions. The structural change and passivation for hard-carbon are investigated to study the reversible sodium insertion. The 3-volt secondary Na-ion battery possessing environmental and cost friendliness, Na+-shuttlecock hard-carbon/NaNi0.5Mn0.5O2 cell, demonstrates steady cycling performance as next generation secondary batteries and an alternative to Li-ion batteries.

Electrochemical Na Insertion and Solid Electrolyte Interphase for Hard-Carbon Electrodes and Application to Na-Ion Batteries

Layered NaNi0.5Mn0.5O2 (space group: R3m), having an O3-type (α-NaFeO2 type) structure according to the Delmas’ notation, is prepared by a solid-state method. The electrochemical reactivity of NaNi0.5Mn0.5O2 is examined in an aprotic sodium cell at room temperature. The NaNi0.5Mn0.5O2 electrodes can deliver ca. 105–125 mAh g–1 at rates of 240–4.8 mA g–1 in the voltage range of 2.2–3.8 V and show 75% of the initial reversible capacity after 50 charge/discharge cycling tests. In the voltage range of 2.2–4.5 V, a higher reversible capacity of 185 mAh g–1 is achieved; however, its reversibility is insufficient because of the significant expansion of interslab space by charging to 4.5 V versus sodium. The reversbility is improved by adding fluoroethylene carbonate into the electrolyte solution. The structural transition mechanism of Na1–xNi0.5Mn0.5O2 is also examined by an ex situ X-ray diffraction method combined with X-ray absorption spectroscopy (XAS). The staking sequence of the [Ni0.5Mn0.5]O2 slabs chang...

Study on the Reversible Electrode Reaction of Na1–xNi0.5Mn0.5O2 for a Rechargeable Sodium-Ion Battery

Electrochemical intercalation activity of layered NaCrO2 vs. LiCrO2

Electrochemical activities of NaNi0.5Mn0.5O2 and NaCrO2, having the analogous layered structure to LiCoO2, were investigated in 1 mol dm-3 NaClO4 propylene carbonate at room temperature. Almost all sodium ions were extracted from the NaNi0.5Mn0.5O2 and NaCrO2 electrodes by galvanostatic oxidation to 4.5 V accompanied with several phase transitions. Layered NaNi0.5Mn0.5O2 electrode showed a highly reversible capacity of 185 mAh g-1 as positive electrode in Na cell in the potential region between 2.5 and 4.5 V versus Na. A NaCrO2 electrode was hardly electroactive after oxidation up to 4.5 V. When galvanostatic cycling was carried in the limited potential domain between 2 and 3.5 V, both electrodes showed discharge capacities of 100 - 120 mAh g-1 with satisfactory capacity retention. Layered LiCrO2 (R-3m) and NaCrO2 (R-3m) possess the quite similar crystal structures and the same transition metal, nevertheless they were inactive and active in Li and Na cells, respectively.

Electrochemically Reversible Sodium Intercalation of Layered NaNi0.5Mn0.5O2 and NaCrO2

Fe 3 O 4 powders with different particle sizes on average (400, 100, and 10 nm) were prepared and characterized by X-ray diffraction, transmission electron microscopy, Mossbauer spectroscopy, and electrochemical methods. To examine the electrochemical activity of Fe 3 O 4 in relation to the particle size effect, galvanostatic cycling tests in aprotic electrolytes containing lithium or sodium ions were conducted. The electrochemical activity was significantly enhanced as the mean particle size decreased. The nanocrystallized Fe 3 O 4 (10 nm) prepared by precipitation method delivered 190 mA h g ―1 of the rechargeable capacity in the voltage range of 2-3 V in a lithium-ion containing electrolyte, whereas the 400 and 100 nm Fe 3 O 4 powders showed 10 and 80 mA h g ―1 of the rechargeable capacity, respectively. An ex situ X-ray diffraction study for the electrochemically cycled samples suggested the partly reversible Fe ion migration from the tetrahedral sites to the octahedral sites with a retained spinel framework structure. The nanocrystallized Fe 3 O 4 as well as α-Fe 2 O 3 were highly electrochemically active in the sodium salt electrolyte. The rechargeable capacity of 160 or 170 mA h g ―1 with excellent capacity retention was obtained for nanocrystalline Fe 3 O 4 or α-Fe 2 O 3 , respectively.

Atsushi Ogata

Papers

Electrochemical Na Insertion and Solid Electrolyte Interphase for Hard-Carbon Electrodes and Application to Na-Ion Batteries

Study on the Reversible Electrode Reaction of Na1–xNi0.5Mn0.5O2 for a Rechargeable Sodium-Ion Battery

Electrochemical intercalation activity of layered NaCrO2 vs. LiCrO2

Electrochemically Reversible Sodium Intercalation of Layered NaNi0.5Mn0.5O2 and NaCrO2

Electrochemical Insertion of Li and Na Ions into Nanocrystalline Fe3O4 and α‐Fe2O3 for Rechargeable Batteries