Polyvinylpyrrolidone-Induced Uniform Surface-Conductive Polymer Coating Endows Ni-Rich LiNi_0.8Co_0.1Mn_0.1O₂ with Enhanced Cyclability for Lithium-Ion Batteries

Abstract

The Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode has attracted great interest owing to its low cost, high capacity, and energy density. Nevertheless, rapid capacity fading is a critical problem because of direct contact of NCM811 with electrolytes and hence restrains its wide applications. To prevent the direct contact, the surface inert layer coating becomes a feasible strategy to tackle this problem. However, to achieve a homogeneous surface coating is very challenging. Considering the bonding effect between NCM811, polyvinylpyrrolidone (PVP), and polyaniline (PANI), in this work, we use PVP as an inductive agent to controllably coat a uniform conductive PANI layer on NCM811 (NCM811@PANI–PVP). The coated PANI layer not only serves as a rapid channel for electron conduction, but also prohibits direct contact of the electrode with the electrolyte to effectively hinder side reaction. NCM811@PANI–PVP thus exhibits excellent cyclability (88.7% after 100 cycles at 200 mA g–1) and great rate performance (152 mA h g–1 at 1000 mA g–1). In situ X-ray diffraction and in situ Raman are performed to investigate the charge–discharge mechanism and the cyclability of NCM811@PANI–PVP upon electrochemical reaction. This surfactant-modulated surface uniform coating strategy offers a new modification approach to stabilize Ni-rich cathode materials for lithium-ion batteries.

Surface Modification Strategies for Improving the Cycling Performance of Ni‐Rich Cathode Materials

“…Some coatings can convert these residuals into reasonably conductive lithium compounds, such as phosphates, and garnets, thereby improving the rate capability. It has been claimed that polymeric coatings, which generally achieve full surface coverage more readily, can prevent cracking by giving elastic support to the secondary particles , . Other reported beneficial effects of coatings include suppression of transition‐metal dissolution and improved thermal stability , .…”

“…A good example is the study by Gan et al, where a conducting polymer coating was employed to improve the electrochemical cycling stability of NCM811 (Figure ). The polymer is a composite of polyvinylpyrrolidone (PVP), which binds to the NCM surface, and very stable and electronically conductive polyaniline (PANI).…”

“…Schematic illustration of the preparation of NCM811@PANI–PVP (top) as well as plot of the cycling performance data and cross‐sectional TEM and top‐view SEM images of the coated surface and secondary particles, respectively (bottom). Reproduced with permission from ref . Copyright (2019) American Chemical Society.…”

“…According to the authors, a “stretchy” and uniform coverage is achieved (Figure d as ideal representation) that can withstand cycling‐induced stress for some time. Gan et al also coated a uniform layer of PANI on the surface of Ni‐rich NCM via a crosslinking process in the presence of a surfactant (PVP). The improvement in structural stability of the modified CAM was confirmed by XRD and Raman spectroscopy upon (de)lithiation.…”

Advances and Prospects of Surface Modification on Nickel‐Rich Materials for Lithium‐Ion Batteries†

“…Whereas, the evaporation and decomposition of organics at annealing process limit the variety of coating materials. Recently, the organics used in nickel‐rich materials mainly include polypyrrole, [ 99 ] polyvinylpyrrolidone, [ 100‐101 ] N , N ‐dimethylpyrrolidinium methyl sulfonate, [ 102 ] tetraethyl orthosilicate, [ 103 ] and other conducting polymers. [ 104‐105 ] The excellent electrical conductivity of organics greatly reduces the electrode impedance and improves the electrochemical performance, even at low temperatures.…”