Elsevier

Journal of Power Sources

Volume 196, Issue 23, 1 December 2011, Pages 10222-10227
Journal of Power Sources

LiCr0.2Ni0.4Mn1.4O4 spinels exhibiting huge rate capability at 25 and 55 °C: Analysis of the effect of the particle size

https://doi.org/10.1016/j.jpowsour.2011.08.069Get rights and content

Abstract

The comparison of the rate capability of LiCr0.2Ni0.4Mn1.4O4 spinels synthesized by the sucrose aided combustion method at 900, 950 and 1000 °C is presented. XRD and TEM studies show that the spinel cubic structure remains unchanged on heating but the particle size is notably modified. Indeed, it increases from 695 nm at 900 °C to 1465 nm at 1000 °C. The electrochemical properties have been evaluated by galvanostatic cycling at 25 and 55 °C between 1 C and 60 C discharge rates. At both temperatures, all samples exhibit high working voltage (∼4.7 V), elevated capacity (∼140 mAh g−1) and high cyclability (capacity retention ∼99% after 50 cycles even at 55 °C). The samples also have huge rate capability. They retain more than 70% of their maximum capacity at the very fast rate of 60 C. The effect of the particle size on the rate capability at 25 and at 55 °C has been investigated. It was demonstrated that LiCr0.2Ni0.4Mn1.4O4 annealed at 900 °C, with the lowest particle size, has the best electrochemical performances. In fact, among the LiNi0.5Mn1.5O4-based cathodes, SAC900 exhibits the highest rate capability ever published. This spinel, able to deliver 31,000 W kg−1 at 25 °C and 27,500 W kg−1 at 55 °C is a really promising cathode for high-power Li-ion battery.

Highlights

► Synthesized LiCr0.2Ni0.4Mn1.4O4 spinels exhibit the highest rate capability among LiNi0.5Mn1.5O4-based cathodes. ► The rate capability is enhanced at 25 and 55 °C on decreasing the particle size. ► LiCr0.2Ni0.4Mn1.4O4 heated at 900 °C delivers a high power of 31,000 W kg−1. ► LiCr0.2Ni0.4Mn1.4O4 at 900 °C is a really promising cathode for commercial Li-ion batteries.

Introduction

The electrification of the road transport, i.e. the wide use of electric vehicles (EVs), is one of the more straightforward ways to combat three of the most important challenges of the XXI century: (i) climatic change, (ii) increased pollution in large cities and (iii) strong dependence on fossil fuels. A key factor for EVs is the battery which must combine high energy and power with low pollution and cost [1]. Nowadays, lithium-ion batteries (LIBs) are the technology of choice to drive the EVs [1], [2], [3]. A major challenge in LIBs is to develop new electrode materials with power capabilities close to that of supercapacitors (∼10 kW kg−1) [4], [5], [6]. To reach this goal, several strategies are being developed. For instance (i) doping popular electrode materials such as LiCoO2 [7], [8] and LiMn2O4 [9], [10], (ii) coating the active materials such as carbon coated LiFePO4 [5], [11] or ZnO coated LiNi0.5Mn1.5O4 spinel [12] and (iii) tailoring the particle size of the electrode materials [2], [3], [13], [14], [15]. Probably, the latter strategy is the most followed because it has been widely demonstrated that the power output of LIBs can be notably increased by reducing the particle size, i.e. decreasing the Li+-diffusion pathways.

Among the cathode materials under study, LiMn2O4 type spinels (LMS) are one of the most promising candidates for the large-size LIBs needed for electrical vehicles. The main advantages are their low cost and environment friendliness [1], [9], [16], [17]. LMS-type oxydes have a cubic spinel structure, space group Fd-3 m [9], [17], [18]. It can be described as a close-cubic packed of O2− anions in which the Li+ cations are placed in the 8a tetrahedral positions and the manganese and dopant metal cations (M) are situated in the 16d octahedral sites. The [Mn,M]2O4 framework defines a three-dimensional network of channels through which the Li+ cations can be reversibly de-/inserted. Among the LMS-types cathodes, those derived of the spinel LiNi0.5Mn1.5O4 (LNMS) has been intensively studied since Zhong et al. [19] showed that LNMS was able to de-/inserted Li+ ions at very high potential (∼4.7 V vs. Li+/Li) [20], [21], [22], [23]. Moreover, LNMS-type cathodes show high reversible capacities (∼135 mAh g−1) at room temperature [21], [24], [25]. Unfortunately, the electrochemical performances of these cathodes notably worsen at elevated temperature (∼55 °C) [12], [22], [26], [27]. The development of new strategies to overcome this serious drawback is nowadays one of the most active research lines in the field of advanced cathodes for LIBs. We showed that it is possible to enhance the electrochemical performance of LNMS by doping with chromium. Among the LiCr2yNi0.5−yMn1.5−yO4 spinels synthesized, the sample with y = 0.1 (LiCr0.2Ni0.4Mn1.4O4) exhibited the best electrochemical performances [28]. Furthermore, we demonstrated that cycleability at 25 and at 55 °C of the LiCr0.2Ni0.4Mn1.4O4 spinel strongly depended on the particle size [27]. The samples synthesized at T  900 °C, with particle size >690 nm, shown a remarkable cycling performance even when cycling was performed at elevated temperature (55 °C). In this paper, we report the effect of particle size of the LiCr0.2Ni0.4Mn1.4O4 spinel annealed at T  900 °C on its rate capability and its specific power at 25 and 55 °C.

Section snippets

Experimental/materials and methods

The “as-prepared” LiCr0.2Ni0.4Mn1.4O4 spinel was synthesized by the sucrose aided combustion method previously described [28]. Three LiCr0.2Ni0.4Mn1.4O4 samples have been prepared by annealing for 1 h the “as-prepared” spinel at 900, 950 and 1000 °C being the heating/cooling rate of 2 °C min−1. The samples are labeled as “SACNumber” where SAC and Number stand for Sucrose Aided Combustion and for the annealing temperature, respectively.

The analysis of the phase purity and the structural

Result and discussion

The structural characterization of the SAC-samples was carried out by X-ray diffraction. The corresponding patterns, given in Fig. 1, indicate that single phase spinels were obtained for the three annealing temperatures. The absence of the (2 2 0) diffraction peak around 2θ = 30° indicates that there is no transition metal ions in the 8a tetrahedral positions. The cubic unit cell parameter (ac) for the SAC-spinels is summarized in Table 1. The likeness of the ac-values indicates that the cubic

Conclusion

LiCr0.2Ni0.4Mn1.4O4 cathode materials have been prepared by the sucrose aided combustion method followed by thermal treatments at 900, 950 and 1000 °C. The structural study shows that SAC-samples are single-phase cubic spinel. They have similar unit cell parameter (ac  8.189 Å) indicating that there is no structural modification on heating. The morphological characterization by TEM evidences that the main effect of the thermal treatment is the remarkable growth of the particle size from 695 nm at

Acknowledgments

Financial support through the projects MAT2008-03182 (MICINN), MATERYENER P2009/PPQ-1626 (CAM) and 2009MA0007 (CSIC/CNRST) are gratefully recognized. M. Aklalouch thanks the AECI for the MAEC-AECI fellowship.

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