Insight into the capacity fading of layered lithium-rich oxides and its suppression via a film-forming electrolyte additive

Abstract

The capacity fading of layered lithium-rich oxide (Li1.2Mn0.54Ni0.13Co0.13O2, LLO) cathodes greatly hinders their practical application in next generation lithium ion batteries.

Significance of Electrolyte Additive Molecule Structure in Constructing Robust Interphases on High-Voltage Cathodes

“…31−33 After the 120th cycle, the discharge capacity drops dramatically and a capacity retention of only 23.8% is achieved at the 175th cycle, which should be mainly ascribed to the structure destruction of the generated spinel phase owing to massive Mn dissolution from LRO. 21,31 It has been known that oxygen evolution from LRO takes place under high voltage, which will oxidize the electrolyte to produce various byproducts: gaseous species such as CO 2 , CO, and deposited polymers on LRO surface. 25 Besides, HF is formed from the decomposition of LiPF 6 , which will corrode LRO and bring about the structure destruction of the generated spinel phase of LRO.…”

“…31−33 Apparently, a protective interphase can be constructed by TMB and TPB, which mitigates the structure transformation of LRO and electrolyte component decomposition. 21,26,40 However, TMB and TPB yield different contributions, with TMB constructing a more stable and robust interphase than TPB. Both TMB and TPB are borates but contain different alkyl groups in the molecule structure, methyl for TMB and propyl for TPB, suggesting that the molecule structure of an electrolyte additive plays a significant role in constructing a stable and robust interphase.…”

“…16−19 The oxygen will oxidize electrolyte components, solvents (organic carbonates), and salt (LiPF 6 ), yielding gaseous products such as CO 2 and CO, polymers that deposit on cathode, and acidic species such as hydrofluoric acid (HF) that are corrosive to cathode and cause transition-metal dissolution and the crystal structure deterioration of cathode. 20,21 To resolve these issues, various approaches have been developed. 22 The most investigated ones are coating and doping.…”

“…20,21,26 Comparatively, the cathode interphase constructed by Bcontaining additives is more conductive for lithium-ion transportation because B tends to combine with F − and reduce the formation of LiF. 21 Unfortunately, the state-of-theart applications of electrolyte additives lack rationality because less knowledge is available on the relationship between the additive molecule structure and interphase stability. In this work, we uncover the significance of the additive molecule structure in constructing a stable and robust interphase.…”

Future Material Developments for Electric Vehicle Battery Cells Answering Growing Demands from an End-User Perspective

“…This gap in terms of material performance was first discussed for Li 2 MnO 3 [121]. Several mechanisms were considered at charging voltages ≥ 4.5 V vs. Li/Li + , from oxide decomposition via oxygen evolution [122] to phase transformation [123,124] and oxidation of the non-aqueous electrolyte [125]. Recent reports demonstrate that a reversible and stable anionic capacity is feasible for the oxides [126] requiring fine-tuning of the chemical compositions, in addition to stable electrolytes at high voltages.…”