A review on the stability and surface modification of layered transition-metal oxide cathodes

Abstract

An ever-increasing market for electric vehicles (EVs), electronic devices and others has brought tremendous attention on the need for high energy density batteries with reliable electrochemical performances. However, even the successfully commercialized lithium (Li)-ion batteries still face significant challenges with respect to cost and safety issues when they are used in EVs. From a cathode material point of view, layered transition-metal (TM) oxides, represented by LiMO 2 (M = Ni, Mn, Co, Al, etc.) and Li-/Mn-rich xLi 2 MnO 3 Á(1-x)LiMO 2 , have been considered as promising candidates because of their high theoretical capacity, high operating voltage, and low manufacturing cost. However, layered TM oxides still have not reached their full potential for EV applications due to their intrinsic stability issues during electrochemical processes. To address these problems, a variety of surface modification strategies have been pursued in the literature. Herein, we summarize the recent progresses on the enhanced stability of layered TM oxides cathode materials by different surface modification techniques, analyze the manufacturing process and cost of the surface modification methods, and finally propose future research directions in this area.

Improved Cycling Stability of LiNi0.8Co0.1Mn0.1O2 Cathode Material via Variable Temperature Atomic Surface Reduction with Diethyl Zinc

“…It is fair to assume that our present work is very similar to Elam and Greeley, but with deeper penetration of the Zn 2+ at vacant interstitial vacant sites (we have used diethyl zinc as a reducing precursor, instead of trimethyl aluminum). We propose that our surface treatment process at 200 °C in argon atmosphere results in the partial transformation of surface spinel structure in NCM811, as previously reported to happen under similar conditions [ 31 ] and that this transformation facilitated the interstitial diffusion of Zn 2+ into the crystal lattice sites in surface and subsurface region. Additional reduction of Ni sites also supports the above mechanism (Figure 2b).…”

A Review of Degradation Mechanisms and Recent Achievements for Ni‐Rich Cathode‐Based Li‐Ion Batteries

“…Numerous efforts have been devoted to the performance improvement for Ni‐rich cathode‐base LIBs. [ 105,106 ] The current strategies primarily focus on modifying the cathode, anode, and electrolyte. For cathode materials, the proposed strategies can be divided into the following categories: 1) Applying novel synthesis methods to avoid side‐effects induced by conventional coprecipitation methods; 2) fabricating single‐crystallized primary particles in favor of mitigating inner stress during the (de)lithiation process; 3) tailoring highly ordered morphologies to inhibit microcracks propagation within the electrode particles; 4) introducing foreign ions (cations or anions) into the crystal lattice for structural stabilization of the host material; 5) coating protective layers onto the cathode surface to prevent HF attack from the electrolyte; and 6) synthesizing particles with elemental concentration gradient structure.…”

“…Numerous organic materials have also been investigated to suppress electrolyte decomposition at the cathode electrode surface. [ 105 ] Park and co‐workers developed an OTS‐coated (octyltrichlorosilane) LiNi 0.82 Mn 0.09 Co 0.09 O 2 (NCM82) cathode with higher storage cyclability. [ 156 ] The OTS molecules homogeneously self‐assembled via van der Waals forces into a monolayer on the NCM82 surface, as depicted in Figure 25d.…”

Impact of Surface Coating on the Low Temperature Performance of a Sulfide-Based All-Solid-State Battery Cathode

“…It is speculated that the low value of R2, even in the absence of the coating (bare), is due to residual lithium compounds, such as LiOH and Li2CO3, which sre particular to the NCM surface. 19 Although it was difficult to quantify the absolute amount, the surface carbonate concentration of bare NCM523 by X-ray photoelectron spectroscopy (XPS) analysis was ~15 at%. In contrast, the dramatic decrease in R3 and associated activation energy in the coated sample was most likely caused by the suppression of the side reactions, such as elemental exchange 20 and the formation of a space charge layer (depletion layer).…”