Surface Engineering and Trace Cobalt Doping Suppress Overall Li/Ni Mixing of Li-rich Mn-based Cathode Materials

Abstract

To supress Li/Ni mixing, the strategy of surface modification and Co doping is proposed. Doping trace Co can suppress Li/Ni mixing in the bulk phase of cathode particles, while the rock-salt shell of a cathode originally containing a large amount of Li/Ni mixed rows can be transformed into a cation-ordered spinel phase and a layered phase on the inside by means of surface engineering. Simultaneously, as a coating layer, the Li2MoO4 nanolayer forms on the surface. With the improved Li-ion diffusion, certain inhibitory effects on voltage attenuation and capacity loss are found. It shows that the surface modification with trace Co dopants greatly reduces the Li/Ni mixing level in the material, beneficial to improving the electrochemical performance. As expected, the Li-rich Mn-based cathode material with a low level of overall Li/Ni mixing shows an initial discharging capacity of 303 mAh g–1. This indicates that the joint application of doping and surface coating effectively enhances the performance of the cathode materials with an ultra-low dosage of Co. This idea is helpful to structure other layered cathode materials by surface engineering.

Functional Composite Dual‐Phase In Situ Self‐Reconstruction Design for High‐Energy‐Density Li‐Rich Cathodes

“…From Figure 3b, LRO‐700 shows poor reversible capacity but outstanding stability due to the excessive electrochemical inactive MO‐type rock‐salt phase reduced capacity while protecting material interfaces. [ 54,55 ] In a word, LRO‐500 with controlled MO‐type phase content has a greater comprehensive performance among LRO‐400 (spinel‐only reconstructed surface) and LRO‐700 (excessive MO‐type rock‐salt reconstructed surface), indicating that the synergistic effect of MO‐type rock‐salt and spinel phase is the main reason for the improvement of LRO‐500. Compared to studies that only coated spinel phase [ 56–58 ] or rock‐salt phase, [ 59 ] this work showed much better cyclic performance.…”

Improved Electrochemical Performance of Li-Rich Cathode Materials via Spinel Li2MoO4 Coating

“…The activation of the Li 2 MnO 3 phase is accompanied by the irreversible release of O 2 , which only occurs during the first charge–discharge cycle. Therefore, in the subsequent cycles, the oxidation peak near 4.7 V disappears [ 39 ], which is also the reason for the low initial Coulombic efficiency of Li-rich materials.…”

Fast Charge-Transport Interface on Primary Particles Boosts High-Rate Performance of Li-Rich Mn-Based Cathode Materials

“…are drawing tremendous attention due to their low cost and high specific discharge capacity (>270 mAh g –1 ). , In electrochemistry, Li-rich Mn-based cathode materials possess higher electrochemical windows and charge compensation provided by transition metal cations and anions jointly at high charging potentials, being derived from the anionic redox reaction in the form of peroxide-like dimers (O 2– /O – ) and irreversible capacity loss in the form of surface lattice oxygen release. − However, it is a double-edged sword. The irreversible oxygen release during the first cycle of activation triggers a detrimental structural transition that gradually diffuses from the particle surface into the bulk while it further deteriorates the reaction kinetics and structural stability, ultimately resulting in poor rate performance and a shortened cycle lifespan. , In the highly delithiated state, the phase transformation from a layered structure to a spinel-like structure of the cathode material caused by the irreversible oxygen loss at elevated temperature can also lead to a decline in thermal stability …”

“…The irreversible oxygen release during the first cycle of activation triggers a detrimental structural transition that gradually diffuses from the particle surface into the bulk while it further deteriorates the reaction kinetics and structural stability, ultimately resulting in poor rate performance and a shortened cycle lifespan. 9,10 In the highly delithiated state, the phase transformation from a layered structure to a spinel-like structure of the cathode material caused by the irreversible oxygen loss at elevated temperature can also lead to a decline in thermal stability. 11 To meet the challenges, numerous modification approaches such as surface coating, ion doping, and morphology controlling have been made in the past decades.…”