Urea-assisted hydrothermal synthesis of a hollow hierarchical LiNi_0.5Mn_1.5O₄ cathode material with tunable morphology characteristics

Abstract

A hollow hierarchical LiNi 0.5 Mn 1.5 O 4 cathode material has been synthesized via a urea-assisted hydrothermal method followed by a high-temperature calcination process. The effect of reactant concentration on the structure, morphology and electrochemical properties of the carbonate precursor and corresponding LiNi 0.5 Mn 1.5 O 4 product has been intensively investigated. The as-prepared samples were characterized by XRD, FT-IR, SEM, CV, EIS, GITT and constant-current charge/discharge tests. The results show that all samples belong to a cubic spinel structure with mainly Fd3m space group, and the Mn 3+ content and impurity content initially decrease and then increase slightly with the reactant concentration increasing. SEM observation shows that the particle morphology and size of carbonate precursor can be tailored by changing reactant concentration. The LiNi 0.5 Mn 1.5 O 4 sample obtained from the carbonate precursor hydrothermally synthesized at a reactant concentration of 0.3 mol L À1 exhibits the optimal overall electrochemical properties, with capacity retention rate of 96.8% after 100 cycles at 1C rate and 10C discharge capacity of 124.9 mA h g À1, accounting for 99.9% of that at 0.2C rate. The excellent electrochemical performance can be mainly attributed to morphological characteristics, that is, smaller particle size with homogeneous distribution, in spite of lower Mn 3+ content. IntroductionLithium ion batteries (LIBs) are being intensively pursued for high-power and high-energy applications such as electric vehicles (EVs) and hybrid electric vehicles (HEVs). 1,2 The energy density of LIB is generally limited by the cathode material. One practical and cost-effective way to improve the energy density of cathode material is elevating the working voltage. Among all cathode materials, LiNi 0.5 Mn 1.5 O 4 spinel has been regarded as one of the most promising cathodes for LIB, owing to high working voltage (4.7 V vs. Li/Li + ) and high energy density (650 W h kg À1 ). 3,4 In addition, the inherently fast Li + ion diffusion within its 3D spinel structure leads to good rate capability and cycling stability. 5 However, simultaneously achieving satisfactory cyclability and rate performance for LiNi 0.5 Mn 1.5 O 4 remains challenging due to complex performance-inuencing factors and electrolyte/structure instability under high potential. 6,7To date, there are three main approaches to solve the above problem, such as surface modication, cation doping and particle size reduction to nanoscale level. The nanosized materials generally show improved rate performance by shorter Li + ion diffusion channel and larger surface area.Unfortunately, low thermodynamic stability of nanoparticles results in electrochemical agglomeration and raises the risk of side reaction with electrolyte, thus leading to inferior cycling stability. 8,9 Recently, the cathodes with hierarchical hollow structure have attracted considerable interests for the coimprovement of rate capability and cycle performance. 10,11On the one hand, this kind...

Scope and significance of transition metal oxide nanomaterials for next-generation Li-ion batteries

“…127 Hydrothermal method allows the usage of various chelating/precipitating agents and varying solvents, such as ethylene glycol, ethanol, and a mixture of versatile solvents to control the ionic concentration of anions that determine the final material composition. 93,124,128,129 X. Qin et al demonstrated the solvent-modified preparation of LiNi 0.5 Mn 1.5 O 4 material using ethylene glycol. 128 From Fig.…”

“…93,124,128,129 X. Qin et al demonstrated the solvent-modified preparation of LiNi 0.5 Mn 1.5 O 4 material using ethylene glycol. 128 From Fig. 10a, the hollow particle morphology's clear homogeneous distribution reveals the nanoscale wall structure while the whole material size averages B3 mm.…”

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