Enabling Superior Electrochemical Performance of Lithium-Rich Li_1.2Ni_0.2Mn_0.6O₂ Cathode Materials by Surface Integration

Abstract

Lithium-rich cathode oxides exhibit extraordinary specific capacities that are mainly ascribed to the accumulated redox reactions of anions and cations at high operating potentials. However, rapid capacity fading and voltage decay have been impeding the commercialization process. Herein, we report a surface integration strategy to improve the capacity and voltage stability of a Co-free lithium- and manganese-rich (LMR) cathode oxide Li1.2Ni0.2Mn0.6O2, by which the spinel phase and surface cobalt gradient doping are synchronously built on the surface of LMR microspheres. The spinel phase and surface cobalt gradient doping surface integration inhibit irreversible phase transformation (layered to spinel or rock-salt structure), promote lithium-ion diffusion, and improve the LMR cathode surface stability. This surface integration design enables a striking reversible discharge capacity of 280.05 mA h g–1 at 0.1 C and a superior cycling performance with a retention of 94.56% at 0.5 C after 200 cycles. Besides, the modified LMR cathode still exhibits an excellent specific capacity of 127.06 mA h g–1 at 10 C. This surface integration strategy opens a new scope for lithium-ion batteries with high energy density for practical applications in the near future.

New Insight into High-Rate Performance Lithium-Rich Cathode Synthesis through Controlling the Reaction Pathways by Low-Temperature Intermediates

“…The LMLO cathode was prepared by a coprecipitation route followed by high-temperature solid reaction. The Ni 0.25 Mn 0.75 CO 3 precursor was prepared by the coprecipitation method as our group’s previous work . Next, the prepared Ni 0.25 Mn 0.75 CO 3 precursor was mixed with the lithium source (LiOH or Li 2 CO 3 ) with a molar ratio of Li:transition metal of 1.5:1 and calcined in air at 500 °C for 5 h and 850 °C for 12 h to obtain the target LMLO product, which was denoted as C–LOH and C–LCO, respectively.…”

“…The Ni 0.25 Mn 0.75 CO 3 precursor was prepared by the coprecipitation method as our group's previous work. 33 Next, the prepared Ni 0.25 Mn 0.75 CO 3 precursor was mixed with the lithium source (LiOH or Li 2 CO 3 ) with a molar ratio of Li:transition metal of 1.5:1 and calcined in air at 500 °C for 5 h and 850 °C for 12 h to obtain the target LMLO product, which was denoted as C−LOH and C−LCO, respectively. To ensure the same Li/M ratio under the initial conditions, inductively coupled plasma atomic emission spectroscopy (ICP-OES) was used to detect the content of Ni, Mn, and Li.…”

“…Recently, many efforts have focused on improving the cycling performance and rate capability of LMLO cathodes, including element doping, coating and defect structures, and surface new phases, etc. − The introduction of the spinel phase into lithium-rich cathode materials has attracted widespread attention. ,,,,− Our recent work indicated that the spinel-layer transition structure can be constructed by Co ion doping to realize the improvement of lithium-ion diffusion and conductivity . The gas–solid treatment which is based on the thermal decomposition of ferrous oxalate oxides also realized the construction of a spinel layer with oxygen vacancies on the surface .…”

“…10,11,16,24,31−38 Our recent work indicated that the spinel-layer transition structure can be constructed by Co ion doping to realize the improvement of lithium-ion diffusion and conductivity. 33 The gas−solid treatment which is based on the thermal decomposition of ferrous oxalate oxides also realized the construction of a spinel layer with oxygen vacancies on the surface. 32 In another work, a controllable oxidation strategy to realize spinel structure coating in LMLO cathodes was proposed, where the transition metal near the surface was oxidized by KMnO 4 to form a nanoscale MnO 2 layer and then converted to Mn-based Li 4 Mn 5 O 12 spinel structures.…”

Significant Enhancement of the Capacity and Cycling Stability of Lithium-Rich Manganese-Based Layered Cathode Materials via Molybdenum Surface Modification

“…To address the above stated problems, many efforts have been devoted to improving the performance of the materials, such as morphology control [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ], surface modification [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ], heteroelements doping [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ], etc. Among them, newly emerged surface modification is regarded as the most effective way to mitigate phase transition triggered by oxygen release and electrolytes etching.…”