Cathode Electrolyte Interface Engineering by Gradient Fluorination for High‐Performance Lithium Rich Cathode

Abstract

Despite their ultrahigh specific capacity, lithium‐rich layered oxide cathodes are still plagued by challenges such as poor cycle stability and notorious voltage decay, which are primarily attributed to surface issues such as the release of lattice oxygen and interfacial side reactions. In this study, a facial strategy of gradient fluorination is adopted to construct a thin but robust LiF‐rich cathode electrolyte interface (CEI), highly enhancing the stability of the interface of lithium‐rich oxides. Experimental results and theoretical calculations both demonstrate that the stable CEI not only promotes oxygen participation in redox reactions and simultaneously inhibits oxygen release and structural transition, but also facilitates the transport kinetics of lithium ions. As a result, the gradient fluorinated lithium‐rich cathode delivers highly enhanced rate performance (133 mAh g−1 at 5 C), superior cycling stability with a capacity retention of 81.9% after 100 cycles at 1 C (250 mAh g−1), and alleviated voltage fade (only 1.75 mV per cycle). Moreover, a unique formation mechanism for LiF‐rich surfaces is proposed according to theoretical calculations. This work not only provides a fresh understanding of the CEI formation mechanism, but also show a promising avenue for designing LiF‐rich CEIs applicable to other layered oxide cathodes.

Construction of LiNi0.5Mn1.5O4 Spinel Layer-Bearing Heterostructural Li-Rich Layered Oxide Cathodes with Enhanced Structural Integrity and Cycling Stability

“…The surface of the cathode will generate a CEI film upon initiating the charging and discharging process. When the CEI film is completely generated into a stable interfacial film, the transmission of lithium ions tends to be stabilized, which in turn reduces the charge transfer resistance. − …”

Tuning the Interface Stability of Nickel-Rich NCM Cathode Against Aggressive Structural Collapse via the Synergistic Effect of Additives

“…The peak intensity of LiF derived from LiDFP + BVM dual-additives electrolyte is much stronger than baseline electrolyte. As LiF has been generally considered an ideal interfacial component to enhance Li + transfer kinetics between cathode and electrolyte, the cycling performance of NCM95 cathodes on LiDFP + BVM electrolytes was then improved remarkably, as aforementioned. It has been reported that a certain amount of Li x PO y F z and Li 3 PO 4 deposited on the surface to compose CEI could be beneficial to cathode structural stability and ionic conductivity. , As shown in Figure d of the P 2p spectrum, the characteristic peaks of Li x PO y F z and Li 3 PO 4 located around 134 eV increase rapidly due to the preferential decomposition of the LiDFP + BVM dual additives in comparison with baseline electrolyte, which is in accordance with the interfacial improvement of NCM95 cathodes incorporated into the LiDFP + BVM electrolyte.…”

“…The peak intensity of LiF derived from LiDFP + BVM dual-additives electrolyte is much stronger than baseline electrolyte. As LiF has been generally considered an ideal interfacial component to enhance Li + transfer kinetics between cathode and electrolyte, 43 the cycling performance of NCM95 cathodes on LiDFP + BVM electrolytes was then improved remarkably, as aforementioned. It has been reported that a certain amount of Li x PO y F z and Li 3 PO 4 deposited on the surface to compose CEI could be beneficial to cathode structural stability and ionic conductivity.…”

Multifunctional Ho2O3 Coating with Oxygen Vacancies Enables High-Performance Lithium-Rich Layered Oxide Cathodes

“…On the one hand, the Ho 2 O 3 coating can reduce the corrosion from the electrolyte on the material, reduce the dissolution of TM, and improve the structural stability of the material. On the other hand, the abundance of oxygen vacancies in the modified material can enhance oxygen binding and reduce oxygen release …”