Synthesis of Li(Co0.8Ni0.2−yAly)O2 (y  0.02) by combustion method as a possible cathode material for lithium batteries

https://doi.org/10.1016/j.msea.2006.09.104Get rights and content

Abstract

The layered compounds, Li(Co0.8Ni0.2−yAly)O2 (y  0.02) were synthesized by a self-sustaining solution combustion method with hexamethylenetetramine (HMTA) as a fuel. The prepared compounds were characterized by means of XRD, SEM and DSC studies. The precursors were also subjected to thermogravimmety (TG) analysis. Li[Co0.8Ni0.2−yAly]O2 (y  0.02)/Li cells have been assembled and were subjected to cycling studies at different C-rates. The substitution of Al3+-ions has considerably increased the structural and thermal properties of the compound.

Introduction

Although LiCoO2 are employed as a cathode materials for commercially available lithium ion batteries, the relatively high cost of cobalt and lure of large specific capacity have however, led to find alternative materials [1], [2]. The low cost and non-toxicity of lithium manganese oxide materials have drawn the attention of many researchers. Although the LiMn2O4 spinel has been extensively studied, it could store 110 mAh g−1 of charge on cycling. Compound with the formula LiMnO2 has been identified as a potential candidate however it changes from layered structure to spinel upon prolonged cycling [3]. Attempts have also been made to circumvent this problem by partial substitution of Mn by other transition metal elements [4].

Our recent study [5] and other reports [6] clearly reveal that the electrochemical behavior of layered compounds is strongly influenced by the method of preparation, as well as the heat treatments. The crystallinity, phase purity, particle morphology, grain size, surface area, and cation distribution in the spinel structure, all of which can impact on the electrochemical performance of the compound are strongly determined by the synthesis procedure [5], [6]. In order to circumvent intensive procedures like repeated grinding and high temperature operations that place in diffusion-solid state reaction method, several innovative low-temperature synthesis procedures have been adopted for the preparation and processing of solid oxide materials [7]. One such approach is combustion synthesis, which involves highly exothermic redox chemical species in flaming (gas-phase), smouldering (heterogeneous), or explosive reactions [8].

This method provides several advantages: simple and economical preparation, easy control of homogeneity and stoichiometry, easy incorporation of dopants/substituents, production of fine-particulate, high surface area materials by virtue of the accompanying gas evolution, and versatility in terms of the variety of fuels that can be used for the synthesis [9], [10]. Although partial substitution of aluminum gives some positive effect on the thermal stability, cycling tests have also shown a decrease of electrochemical performances of the batteries due to the introduction of electro-inactive cations [11], [12]. The partial substitution of nickel in the system has been considered as a good means to combine both positive effects, i.e., an increasing structural characteristics associated with increasing electrochemical properties induced by nickel and an increasing thermal stability by Al [11], [12]. This paper, we present our results on the synthesis, characterization and electrochemical behavior of Li(Co0.8Ni0.2−yAly)O2 synthesized with hexmethylenetetramine (HMTA) as fuel because it has higher reducing value (36), and nitrates of manganese, cobalt, aluminum and lithium as the oxidants.

Section snippets

Experimental procedure

Li(Co0.8Ni0.2−yAly)O2 (y = 0, 0.01 and 0.02) were prepared by self- sustaining solution combustion method [10]. All mixtures had a HMTA: total cation mole ratio of 1:1. Stochiometric amounts of LiNO3, Mn(NO)3·4H2O, Co(NO)3·4H2O and Al(NO)3·9H2O were dissolved in a minimum amount of double distilled water. A viscous gel was obtained upon the evaporation of excess water. The resulting gel was fired at 500 °C, and the decomposed powder was ground and calcined at 950 °C. In order to avoid the loss of

TG-analysis

The thermogram recorded with a dry pellet made from the mixture of LiNO3, Mn(NO)3·4H2O and Co(NO)3·4H2O with HMTA and LiNO3, Mn(NO)3·4H2O, Co(NO)3·4H2O and Al(NO)3·9H2O with HMTA are depicted in Fig. 1(a and b), respectively. The weight loss that occurs from the room temperature to about 120 °C is attributed to loss of superficial water and water loss from the hydration of manganese nitrate tetrahydrate, which normally decomposes above 100 °C. The irreversible decomposition starts and formation

Conclusions

Cycling tests have shown an improvement in the electrochemical properties of Al-doped compound in comparison with the one obtained for the LiNi0.8Co0.2O2 system. Indeed, higher initial discharge capacity and stability during the cycling have been observed. The combined Ni and Al substitution for cobalt appears, therefore, very promising, as they add the positive effect of nickel, with an improvement of the lamellar character for the structure and of the electrochemical properties.

Acknowledgement

This work was supported by the Core Technology Development Program of the Ministry of Commerce Industry and Energy MOCIE.

References (21)

  • G.T.K. Fey et al.

    J. Power Sources

    (2003)
  • N. Tran et al.

    Solid State Ionics

    (2005)
  • K.C. Patil et al.

    Curr. Opin. Solid State Mater. Sci.

    (1997)
  • T. Mimani

    J. Alloys Compd.

    (2001)
  • S.K. Jeong et al.

    Electrochim. Acta

    (2006)
  • G.T.K. Fey et al.

    Mater. Chem. Phys.

    (2006)
  • S.H. Park et al.

    J. Power Sources

    (2003)
  • J.-H. Kim et al.

    Solid State Ionics

    (2003)
  • K.S. Tan et al.

    J. Power Sources

    (2005)
  • P.G. Bruce et al.

    J. Mater. Chem.

    (1999)
There are more references available in the full text version of this article.

Cited by (9)

  • High-voltage cathode materials by combustion-based preparative approaches for Li-ion batteries application

    2020, Journal of Power Sources
    Citation Excerpt :

    In addition, it was later established that the charge transfer resistance is minimum for the stoichiometric composition of LiCo0.8Ni0.2O2, as observed by the electrochemical impedance spectroscopy (EIS) study [55,64]. Further, low Al-doping (y ≤ 0.02) performed on this cathode by a gel-based combustion (with the fuel hexamethyelendiamine (HMTA): total cation in 1:1 mol ratio) led to the formation of a Li(Co0.8Ni0.2−yAly)O2 cathode with improved properties [65]. Whereas, Mg-,Ni–Zn-doped LiCoO2 cathodes maintained the layered rhombohedral structure until a dopant concentration of x = 0.5 while the Mn-substituted LiCoO2 cathode experiences a layered to spinel transformation even at 0.3 ≤ x ≤ 0.5 and leads to a poor electrode cycling performance [66].

  • Electroceramics for Fuel Cells, Batteries and Sensors

    2011, Functional Materials: Preparation, Processing and Applications
View all citing articles on Scopus
1

On deputation from Central Electrochemical Research Institute, Karaikudi 630 006, India.

View full text