Synergistic Strategy Using Doping and Polymeric Coating Enables High-Performance High-Nickel Layered Cathodes for Lithium-Ion Batteries

Abstract

As one of the most promising cathode materials for lithium-ion batteries, nickel-rich layered oxide LiNi0.83Co0.11Mn0.06O2 (NCM83) has an inherent issue with rapid capacity decay caused by phase change and interface side reactions during the charge/discharge cycling. Herein, an effectively synergistic strategy for improving the structural stability and electrochemical performance of NCM83 cathodes has been proposed, combining surface polymeric coating with bulk doping by the high-temperature solid-phase method. The comprehensive results demonstrate that the niobium (Nb) element can be successfully bulk-doped into the crystal lattice, which could increase the layer spacing, thus stabilizing the crystal structure and minimizing the Li+/Ni2+ mixing in the as-prepared NCM83 cathode. Meanwhile, a small amount of Nb in the form of oxide and a layer of polyaniline (PANI) was coated on the NCM83 cathode’s surface. This not only can prevent electrolyte erosion and inhibit side reactions but also can effectively improve the transport coefficient of Li+ during the charge and discharge process. The optimized NCM83 cathode exhibited outstanding discharge-specific capacity (236.79 mAh g–1 at 0.2 C rate and 215.67 mAh g–1 at 2 C rate), stable cycling performance (capacity retention of 84.4% after 100 cycles at 2 C), and excellent rate performance (150.58 mAh g–1 at 10 C) by taking advantage of the synergistic effects. The synergistic strategy using Nb doping in combination with a surface polymeric coating can enhance the fundamental understanding of the high-nickel layered oxide cathodes for lithium-ion batteries.

The role of niobium in layered oxide cathodes for conventional lithium-ion and solid-state batteries

“…The main observed phases in XRD patterns are Li 3 NbO 4 , [116][117][118] LiNbO 3 , 78,104,119 and Nb 2 O 5 , 117 which in general indicates that a solid solution limit was reached and remaining Nb 5+ ions reacted with the available lithium source, as mentioned before for coated CAMs. Therefore, the probable minimal concentration and widespread distribution of these phases in Nbmodified materials hinder their detection with XRD analysis.…”

Effect of Heteroatom Doping on Electrochemical Properties of Olivine LiFePO4 Cathodes for High-Performance Lithium-Ion Batteries

“…The XPS spectra of all samples show typical peaks for C 1s, P 2p, O 1s, Li 1s, and Fe 2p. Figure S11f,g confirm the presence of Nb 3d 5/2 and Nb 3d 3/2 at the 206.64 and 209.39 eV peaks [39,40] and F 1s at the 691.85 eV peak in LFP/C-Nb 1 and LFP/C-F 3 , respectively, signifying the successful doping of F and Nb elements in the LFP/C cathode material.…”

“…A linear correlation of the open–square value of the CV scan rate ( v 1/2 ) with the peak current ( i p ) yields the slopes of the charging and discharging processes (I A and I C ), indirectly representing the Li + diffusion coefficient of the samples ( D Li+ ). For the precise determination of D Li+ , the Randles–Sevcik equation should be used, as shown in Equation (2) [ 39 , 53 , 54 ]. …”

“…Here, n denotes the number of electrons involved in redox reactions; i p represents the peak current (mA); A signifies the electrode geometric area (cm 2 ); D Li+ denotes the Li + diffusion coefficient; C relates to the Li + concentration of (mol cm −3 ); and v corresponds to the potential scan rate (V s −1 ) [ 39 ].…”

“…The impedance fitting results underscore the superior stability of LFP/C–Nb 1 under prolonged cycling. The determination of the Li + diffusion coefficient ( D Li+ ) is outlined in Equations (3)–(5) [ 39 , 57 , 58 , 59 ], which are provided below. …”