In Situ Reconstruction of the Spinel Interface on a Li-Rich Layered Cathode Material with Enhanced Electrochemical Performances through HEPES and Heat Treatment Strategy

Abstract

The layered manganese-based lithium-rich oxide (LLO) cathode material is considered one of the most attractive cathode material candidates for next-generation lithium-ion batteries due to its high specific capacity. However, LLOs suffer from low coulombic efficiency as well as cycle capacity decay due to oxygen release and structural transformation during the first charge. Here, we report a simple method with 2-[4-(2-hydroxyethyl)-1-piperazinyl]­ethanesulfonic acid (HEPES) treatment combined with heat treatment under a H2 atmosphere for LLO to obtain oxygen vacancies and a spinel phase coating layer with a fast lithium-ion diffusion path. The oxygen vacancies can reduce the charge transfer resistance and increase the diffusion ability of lithium ions. The spinel phase coating can accelerate the diffusion of lithium ions at the cathode interface, thus improving the rate performance of LLO materials. The HEPES-treated LLO material with optimization exhibits high initial coulombic efficiency, high discharge capacity, high rate performance, and excellent cycling stability after 200 cycles at 0.5 C, which are attributed to the oxygen vacancy and spinel phase coating. The study provides significant design guidance for the industrialization of LLO cathodes with practically high rate performance and long cycle life.

Simple and Ingenious Manner To Build Li-Rich Layered Materials with Surface Layered/Spinel Heterostructures and Li Deficiencies

“…30 The bending E g and stretching A 1g modes of the LiMO 2 phase can be validated in the peak positons at 485 and 591 cm −1 . 26,31 The Raman profiles of the LR-0 and LR-S samples showed the characteristic peaks of the Li 2 MnO 3 phase and the LiMO 2 component; however, the peaks at around 630−680 cm −1 are generated in the LR-S sample, indicating that the formation of the spinel structure can be confirmed by the Raman test. 26 At the same time, the refined Raman spectra of the LR-S sample showed that the content of the spinel structure in the LR-S sample is 4.67%, as shown in Figure S1 of the Supporting Information.…”

Oxygen vacancy in Li-rich Mn-based cathode materials: origination, influence, regulation and characterization

“…), ion doping (Ce, 19 Nb, 20 S, 21 ) or thermal reduction (H 2 , 22 CO/CO 2 23 ), which can increase the initial Coulombic efficiency, improve the structural stability, and enhance the capacity retention ability. Sun et al 24 reduced part of Li 2 M-nO 3 (P-Li 2 MnO 3 ) to Li 2.1 Mn 0.9 O 2.79 by low-temperature reduction method with stearic acid, so as to introduce stacking faults, Vo and orthorhombic LiMnO 2 structures into the Li 2 MnO 3 phase (R-Li 2 MnO 3 ), and found that the introduction of Vo could not only increase the initial Coulombic efficiency (P-Li 2 MnO 3 : 33.6%; R-Li 2 MnO 3 : 77.1%), but also effectively accelerate the Li + diffusion in the material (P-Li 2 MnO 3 : 6.10 Â 10 À16 cm 2 s À1 ; R-Li 2 MnO 3 : 1.32 Â 10 À15 cm 2 s À1 ).…”

“…In addition, LiBOB 15 and FEC 16 were employed as electrolyte additives to form a stable conductive SEI film, which contributes to the improved interface stability and the alleviated voltage attenuation. Moreover, it has a remarkable significance in the introduction of Vo on the surface or in the bulk for LRMOs by gas–solid reaction (NH 4 HCO 3 , 17 NH 4 BF 4 18 ), ion doping (Ce, 19 Nb, 20 S, 21 ) or thermal reduction (H 2 , 22 CO/CO 2 23 ), which can increase the initial Coulombic efficiency, improve the structural stability, and enhance the capacity retention ability. Sun et al 24 reduced part of Li 2 MnO 3 (P-Li 2 MnO 3 ) to Li 2.1 Mn 0.9 O 2.79 by low-temperature reduction method with stearic acid, so as to introduce stacking faults, Vo and orthorhombic LiMnO 2 structures into the Li 2 MnO 3 phase (R-Li 2 MnO 3 ), and found that the introduction of Vo could not only increase the initial Coulombic efficiency (P-Li 2 MnO 3 : 33.6%; R-Li 2 MnO 3 : 77.1%), but also effectively accelerate the Li + diffusion in the material (P-Li 2 MnO 3 : 6.10 × 10 −16 cm 2 s −1 ; R-Li 2 MnO 3 : 1.32 × 10 −15 cm 2 s −1 ).…”

Limiting voltage and capacity fade of lithium-rich, low cobalt Li1.2Ni0.13Mn0.54Fe0.1Co0.03O2 by controlling the upper cut-off voltage

“…Besides, there is the degradation of the different components of the electrodes such as the binder, conductive additive, and the electrolyte. Several strategies have been adopted to stabilize the crystal structure and decrease the voltage and capacity drop of Li-rich NMC cathode material including surface coating, [31][32][33][34][35][36] doping, 29,[37][38][39][40][41][42][43][44][45] structural modication, [46][47][48][49][50][51][52][53] lithium extraction, [54][55][56][57] and electrolyte modication. [58][59][60][61][62][63][64] Controlling the cut-off voltage can be also an effective strategy for stabilizing the crystal structure and decreasing the capacity and voltage drop of Li-rich NMC cathode materials.…”