An Antiaging Electrolyte Additive for High‐Energy‐Density Lithium‐Ion Batteries

Abstract

critical challenges to be overcome for the successful utilization of Li-rich cathodes in LIBs. Li-rich cathodes suffer from severe voltage decay and continued capacity fading upon repeated cycling mainly because of two unfavorable reactions: 1) the interfacial degradation that stems from an unstable cathode-electrolyte interphase and 2) the irreversible phase transformation from layered to spinel. [9][10][11] Undesirable electrolyte decomposition at the Li-rich cathode with a high operation voltage of 4.4 V versus Li/Li + causes irreparable damage to the cathode-electrolyte interface (CEI), such as inhomogeneous delithiation induced by a nonuniform surface coverage of decomposition byproducts and the consumption of active Li + ions and electrons. [12,13] The second issue, irreversible phase transformation, which is most likely the major reason for voltage decay, is not fully understood. This transformation is closely linked to a reduction in the valence state of transition metal ions in the Li-rich cathode and propagates gradually from the interface to the bulk as the cycle progresses. [11,14] On the basis of the aforementioned reports, at a high voltage, the highly oxidized transition metal ions are prone to take electrons from the electrolyte components to lower their valence state, resulting in their phase transformation from layered to spinel. [15] The formation of a stable CEI by additives can improve the electrochemical performance of Li-rich cathodes while mitigating the sustained occurrence of unfavorable phase transformations through reforming the cathode interface. [16][17][18][19][20] Moreover, the decrease in the valence state of the transition metal ions leads to the release of oxygen (O 2 ) and superoxide radicals (O 2 •− ) to maintain the charge balance in the cathode during subsequent cycling. [21][22][23] Electrochemical activation of Li 2 MnO 3 in a Li-rich cathode above 4.4 V versus Li/Li + on the first charge inevitably evolves reactive oxygen species, including oxygen gas (O 2 ) and superoxide radicals (O 2 •− ), in a cell. [22,24] The reactive superoxide radical (O 2 •− ) generated from the Lirich cathode produces gaseous products such as CO and CO 2 through reaction with the ethylene carbonate (EC) solvent in the electrolyte and accordingly causes a sudden termination of battery operation by electrolyte depletion. [15,25] Therefore, scavenging the reactive oxygen species serves as an effective way to improve the electrochemical performance of Li-rich cathodes.High-capacity Li-rich layered oxide cathodes along with Si-incorporated graphite anodes have high reversible capacity, outperforming the electrode materials used in existing commercial products. Hence, they are potential candidates for the development of high-energy-density lithium-ion batteries (LIBs). However, structural degradation induced by loss of interfacial stability is a roadblock to their practical use. Here, the use of malonic acid-decorated fullerene (MA-C 60 ) with superoxide dismutase activity and water scavenging capabil...

Demystifying the Lattice Oxygen Redox in Layered Oxide Cathode Materials of Lithium-Ion Batteries

“…(B, C) Schematic representation of the degradation of a Li-rich cathode by reactive species and protection of a Li-rich cathode by the MA-C 60 additive as a reactive species scavenger and interface modifier. Adapted with permission from ref . Copyright 2020 Wiley-VCH.…”

“…(D) Schematic illustration showing the H 2 O scavenging effect of the MA-C 60 additive and CEI degradation by the attack of HF at the Li-rich CEI. Adapted with permission from ref . Copyright 2020 Wiley-VCH.…”

Fullerenes for rechargeable battery applications: Recent developments and future perspectives

“…More importantly, such additives are usually highly effective, resulting in a low dosage (generally below 1 wt%), which can alleviate the cost issue of fullerene-based materials. Recently, Kwak et al [67] reported a novel anti-aging electrolyte additive using malonic acid-decorated fullerene (MA-C 60 , adding 1 wt%) for Li-rich cathodes. The MA-C 60 can not only serve as superoxide dismutase activity to inhibit the solvent decomposition but also has excellent water scavenging capability to sustain a long-term, stable cathode electrolyte interface (Fig.…”

Interfacial Degradation and Optimization of Li‐rich Cathode Materials†

“…Han et al . [ 117 ] used a Malonic acid‐decorated fullerene (MA‐C60) that was highly efficient in scavenging superoxide radicals and water. The use of additives can effectively avoid superoxide radical catalyzed electrolytes oxygenation, and prevent the reaction of PF 5 with water to generate corrosive HF, as shown in Figure 9C.…”

“…Copyright 2020, Elsevier B.V. (C) Schematic representation of the degradation of a Li‐rich cathode by reactive species and protection of a Li‐rich cathode by the MA‐C60 additive. Reproduced with permission from Ref [117]. Copyright 2020, WILEY‐VCH.…”