Synthesis of Ordered Mesoporous Li–Mn–O Spinel as a Positive Electrode for Rechargeable Lithium Batteries

Abstract

LiMn 2 O 4 spinel is one of the most important intercalation electrodes for rechargeable lithium batteries at the present time. [1][2][3][4] It combines the highest intrinsic rate capability of the well-known intercalation cathodes with high safety, low toxicity, and low cost, making it attractive for high-power applications, such as hybrid electric vehicles. [5][6][7][8][9][10][11] However, the drawback of this electrode is its slow dissolution in the electrolyte present in the lithium-ion battery. To mitigate such dissolution, recent interest has focused on highly lithium-rich compositions in the region of Li 1. [11,12] Consequently, high rate capability becomes even more important to ensure high utilization of the reduced theoretical capacity. Here we describe the synthesis of an ordered mesoporous Li 1.12 Mn 1.88 O 4 spinel and show that it combines higher rate capability than the corresponding bulk material (50 % higher specific capacity at a rate of 30C, 3000 mA g À1 ) at ambient temperature with good stability at elevated temperatures, despite a high surface area of 90 m 2 g À1 and without the need for deliberate coating or doping with foreign ions. [13,14] Furthermore, when cycled over a wide voltage range (including the 3 V and 4 V plateaus) the mesoporous material exhibits improved capacity retention compared to the bulk spinel. This capacity retention is because of the nanometer thin walls between the pores that render the cubic/tetragonal phase transformation more facile in the mesoporous spinel than in the bulk phase. The potential advantages of using nanostuctured electrode materials, in this case mesoporous solids, over nanoparticles are discussed.Ordered mesoporous Li 1+x Mn 2Àx O 4 spinel is synthesized for the first time, as described in detail in the Experimental Section, by a hard templating route with post-template treatment .[ [15][16][17][18][19] Briefly, an aqueous solution of Mn(NO 3 ) 2 was infiltrated into the ordered 3D pore structure of the mesoporous silica, KIT-6. Heating in air converted the precursor into Mn 2 O 3 . Following the removal of the SiO 2 template, the replica 3D mesoporous Mn 2 O 3 was transformed to Mn 3 O 4 spinel by heating in a reducing atmosphere, which then reacted with LiOH to form mesoporous LiMn 2 O 4 spinel (Figure 1). It is remarkably that throughout the solid-state transformations Mn 2 O 3 !Mn 3 O 4 !LiMn 2 O 4 , the ordered 3D mesoporous structure was preserved (Figure 1), demonstrating that the thin walls of the mesopore (7 nm thick) can accommodate the strain of multiple solid-solid phase transformations. The mesoporous structure exists throughout the material, as demonstrated by examining many particles using

Porous nanoarchitectures of spinel-type transition metal oxides for electrochemical energy storage systems

“…Nanostructured spinel LiMn 2 O 4 has shown a remarkably improved electrochemical performance in comparison with bulk spinel LiMn 2 O 4 . [157][158][159][160][161][162][163][164][165] In particular, porous spinel LiMn 2 O 4 nanostructures showed great promise for further improvement of their electrochemical performance during long-term use. 166 The porous structure generally offers a large active surface, short diffusion lengths of charge carriers (i.e., Li + ), and sufficient electrolyte pathways, which are responsible for improving Li + mobility in the given structure.…”

Microwave-assisted optimization of the manganese redox states for enhanced capacity and capacity retention of LiAlxMn2−xO4 (x = 0 and 0.3) spinel materials

“…High content of Mn 3+ ions causes capacity fading, and leads to the dissolution of the cathode material into the electrolyte. There are three known strategies for improving the cycling performance of LMO; (i) making the spinel structure lithium-rich (Li-excess), [16][17][18] (ii) doping with cations [19][20][21] and (iii) coating with metal oxides. Aluminium is a preferred dopant for LMO [16][17][18] since it is abundant, non-toxic, less expensive and lighter than transition metal elements.…”

Microemulsion‐Assisted Synthesis of Nanosized LiMnO Spinel Cathodes for High‐Rate Lithium‐Ion Batteries

“…[1][2][3][4][5][6][7] However, this material suffers from the drawback of slow dissolution of Mn 2 + into the electrolyte according to the disproportionation reaction: 2 Mn 3 + !Mn 2 + + Mn 4 + , and thus results in a limited cycling stability. To overcome this issue, recent interests have been focused on making samples with lithium-rich compositions (e.g.…”

“…To overcome this issue, recent interests have been focused on making samples with lithium-rich compositions (e.g. Li 1 + x Mn 2Àx O 4 ), [3,[8][9][10][11][12] despite compromising their theoretical capacities. The goal is to raise the valence state of manganese, which minimizes the dissolution of Mn 2 + ions into the electrolyte and also reduces the Jahn-Teller distortion of the lattice structures.…”