In Situ Interfacial Tuning To Obtain High-Performance Nickel-Rich Cathodes in Lithium Metal Batteries

Abstract

Nickel-rich layered oxides are currently considered the most practical candidates for realizing high-energy-density lithium metal batteries (LMBs) because of their relatively high capacities. However, undesired nickel-rich cathode–electrolyte interactions hinder their applicability. Here, we report a satisfactory combination of an antioxidant fluorinated ether solvent and an ionic additive that can form a stable, robust interfacial structure on the nickel-rich cathode in ether-based electrolytes. The fluorinated ether 1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether (TFOFE) introduced as a cosolvent into ether-based electrolytes stabilizes the electrolytes against oxidation at the LiNi0.8Mn0.1Co0.1O2 (NCM811) cathode while simultaneously preserving the electrochemical performance of the Li metal anode. Lithium difluoro­(bisoxalato)­phosphate (LiDFBP) forms a uniform cathode–electrolyte interphase that limits the generation of microcracks inside secondary particles and undesired dissolution of transition metal ions such as nickel, cobalt, and manganese from the cathode into the electrolyte. Using TFOFE and LiDFBP in ether-based electrolytes provides an excellent capacity retention of 94.5% in a Li|NCM811 cell after 100 cycles and enables the delivery of significantly increased capacity at high charge and discharge rates by manipulating the interfaces of both electrodes. This research provides insights into advancing electrolyte technologies to resolve the interfacial instability of nickel-rich cathodes in LMBs.

Three-Dimensional Porous Frameworks for Li Metal Batteries: Superconformal versus Conformal Li Growth

“…Great efforts have been devoted to suppressing the formation of Li dendrites in recent years. For example, functional electrolytes and additives were examined to form stable solid-electrolyte interphase layers. − Protective layers were suggested to mechanically suppress not only the growth of Li dendrites but also the electrolyte decomposition. − Porous frameworks were introduced as current collectors to confine Li deposition in their void space. − Three-dimensional porous frameworks have significant merits over conventional two-dimensional Li metal foils. The large surface area of the porous frameworks reduces the local current density, promoting uniform Li plating. − In addition, the volume change in the framework during charge and discharge is negligible because the Li metal is confined in the pores of the frameworks. , Taking the pack design of Li metal batteries into consideration, the volume change in the Li metal during cycling needs to be sufficiently small; otherwise the battery pack undergoes irreversible deformation during cycling.…”

High-Voltage-Compatible Dual-Ether Electrolyte for Lithium Metal Batteries

“…The carbonate-based organic electrolyte used in the current LIBs has been optimized to maximize the cell performance for lithium transition metal oxide cathodes and graphite anodes but is not suitable for LMBs because of the high reactivity of metallic lithium and low reduction stability of carbonates. − Many studies have been conducted on electrolytes with high compatibility with metallic lithium and high reduction stability, and it has been revealed that the ether-based 1,2-dimethoxyethane (DME) solvent exhibits the best performance in LMBs. − However, due to the lower oxidation stability of DME compared to carbonates, it is difficult to use ethers with commercial cathode materials such as LiCoO 2 and LiNi x Mn y Co 1– x – y O 2 that have a high reaction voltage of approximately 4 V ( vs Li/Li + ). To increase the oxidation stability, a high-concentration electrolyte system has been considered due to the increased oxidation stability of the DME participating in the solvation of lithium ions. − However, increasing salt concentration is directly related to an increase in the viscosity and a decrease in ionic conductivity that result in an increase in the cell resistance and poor rate capability.…”

In Situ Tuning Residual Lithium Compounds and Constructing TiO2 Coating for Surface Modification of a Nickel-Rich Cathode toward High-Energy Lithium-Ion Batteries

“…9,10 It is generally considered that the volume variation of polycrystalline NCM originates from randomly oriented primary particles as the cause of boundary cracks, resulting in the attenuation of capacity and destruction of the overall structure. 11,12 Meanwhile, the pores gradually generated inside polycrystalline NCM will not only increase the contact area at the cathode/ electrolyte interface but also provide reaction sites with the electrolyte, leading to terrible side reactions and safety issues. 13 Moreover, the original layered phase (R3̅ m) is easily induced to transform into a cation disordered spinel (Fd3̅ m) and rock salt phase (Fm3̅ m) because of the de/intercalation of the lithium ion during electrochemical cycling, resulting in the release of lattice oxygen and further breakdown.…”

“…In the past few decades, extensive reports have focused on polycrystalline NCM cathodes due to their high energy density. It needs to point out that such NCM cathode materials generally display micrometer-scale spherical secondary particles (size ≈ 10 μm) formed by submicrometer-level primary particles (size ≈ 300–500 nm). , It is generally considered that the volume variation of polycrystalline NCM originates from randomly oriented primary particles as the cause of boundary cracks, resulting in the attenuation of capacity and destruction of the overall structure. , Meanwhile, the pores gradually generated inside polycrystalline NCM will not only increase the contact area at the cathode/electrolyte interface but also provide reaction sites with the electrolyte, leading to terrible side reactions and safety issues . Moreover, the original layered phase ( R 3̅ m ) is easily induced to transform into a cation disordered spinel ( Fd 3̅ m ) and rock salt phase ( Fm 3̅ m ) because of the de/intercalation of the lithium ion during electrochemical cycling, resulting in the release of lattice oxygen and further breakdown. − To tackle these defects, innovative and effective strategies should be able to tune the crystal structure and morphology to suppress both internal microcrack and structural failure. , …”