Abstract
Abstract Supercapattery is the generic name for hybrids of supercapacitor and rechargeable battery. Batteries store charge via Faradaic processes, involving reversible transfer of localised or zone-delocalised valence electrons. The former is governed by the Nernst equation. The latter leads to pseudocapacitance (or Faradaic capacitance) which may be differentiated from electric double layer capacitance with spectroscopic assistance such as electron spin resonance. Because capacitive storage is the basis of supercapacitors, the combination of capacitive and Nernstian mechanisms has dominated supercapattery research since 2018, covering nanostructured and compounded metal oxides and sulphides, water-in-salt and redox active electrolytes and bipolar stacks of multicells. The technical achievements so far, such as specific energy of 270 Wh/kg in aqueous electrolyte, and charging–discharging for more than 5000 cycles, benchmark a challenging but promising future of supercapattery.
Highlights
Replacing fossil fuels by renewables requires energy storage, for which electrochemical energy storage (EES) devices are a desirable fit because of their modular nature, commercial choices and potentially fossil-comparable energy capacity
The recent growing interests are partly driven by curiosity and exploration of new and improved EES mechanisms, materials and devices beyond SCs and rechargeable batteries (RBs) [16,17,18]
The other and more fundamental reason is related to pseudocapacitance that has been, misused to account for the behaviour of many new transition metal compounds that are capable of Nernstian storage
Summary
Replacing fossil fuels by renewables requires energy storage, for which electrochemical energy storage (EES) devices are a desirable fit because of their modular nature, commercial choices and potentially fossil-comparable energy capacity. Performance wise, RBs offer higher storage capacity than SCs which are better in power capability, energy efficiency, and cycle life. These complementary merits have encouraged development of several hybrid devices, including lithium-ion capacitors, redox capacitors, and pseudocapacitors [5]. Combination of capacitive and lithium storage electrodes was reported in earlier literatures, the term “lithium-ion capacitor” (LIC) first appeared in 2007 [9,10,11,12] Because of their close relation with LIBs, research and development of LICs have progressed fast, along with other ion capacitors [13,14,15]. The other and more fundamental reason is related to pseudocapacitance that has been, misused to account for the behaviour of many new transition metal compounds that are capable of Nernstian storage
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