Multilayer electrolyte cell: A new tool for identifying electrochemical performances of high voltage cathode materials

doi:10.1016/j.elecom.2013.03.031

Electrochemistry Communications

Volume 32, July 2013, Pages 1-4

https://doi.org/10.1016/j.elecom.2013.03.031 Get rights and content

Highlights

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Multilayer electrolyte cell (MEC) was designed & developed as a new research tool
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The MEC successfully reproduced the performance of LiFePO₄
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Origin of capacity fading in LiNi_0.5Mn_1.5O₄ full-cell was studied using the MEC
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The result clearly indicates that Mn dissolution is the main degradation factor
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Future high voltage electrode & electrolyte can be investigated using the MEC

Abstract

Multilayer electrolyte cell (MEC) was designed and developed as a new tool for investigating electrode/electrolyte interfacial reactions in a battery system. The MEC consists of two liquid electrolytes separated by a solid electrolyte which prevents electrolyte crossover while selectively transporting Li⁺ ions. The MEC successfully reproduced the performance of LiFePO₄ comparable with that obtained from coin cells. In addition, the origin of capacity fading in LiNi_0.5Mn_1.5O₄full-cell (with graphite negative electrode) was studied using the MEC. The performance of LiNi_0.5Mn_1.5O₄ MEC full-cell was superior to that of coin full-cell by eliminating the Mn dissolution problem on graphite negative electrode as evidenced by transmission electron microscopyanalysis. The MEC can be a strong tool for identifying the electrochemical performances of future high voltage positive electrode materials and their electrode/electrolyte interfacial reactions.

Graphical abstract

Introduction

The high operation voltage of the positive electrode can be beneficial for electric vehicle (EV) applications because it can reduce the number of cells in a pack and thereby lower overall costs. The LiNi_0.5Mn_1.5O₄ spinel (~ 4.7 V_vs.Li) is one of the promising high voltage positive electrode materials for next generation Li-ion batteries with a good power performance. However, a major challenge for the implementation of LiNi_0.5Mn_1.5O₄ for EV applications is the instability of standard electrolytes at high voltages (> 4.5 V_vs.Li) [1]. In addition, LiNi_0.5Mn_1.5O₄ spinel suffers from the “Mn dissolution” problem that is detrimental to the cycle life of full-cells with graphite negative electrodes [2], [3], [4], [5]. The poor cycle life observed in full-cells has been understood to occur by the loss of active Li⁺ through continuous SEI formation (electrolyte reduction) promoted by Mn reduced on top of the graphite's surface [4], [6], [7]. Unfortunately, the impact of Mn dissolution on the overall capacity fading in the full-cell has not been gauged properly because it is difficult to separate the influence of reductive and oxidative electrolyte decomposition using traditional cell designs (i.e. coin cells).

In this study, a multilayer electrolyte cell (MEC) was designed and developed as a new tool for investigating electrode/electrolyte interfacial reactions in a battery system. The MEC consists of two liquid electrolytes (L.E.) separated by a solid electrolyte (S.E.) which selectively transports Li⁺ ions illustrated in Fig. 1 (a). This design offers the benefit of isolating the individual positive and negative electrode/electrolyte interfacial reactions in a single cell which cannot be realized by conventional cell designs (i.e. coin cell). Here, the stability of battery performance using the MEC was examined using LiFePO₄ as the positive electrode material. In addition, attempts to identify the origin of capacity fading and the impact of Mn dissolution in a LiNi_0.5Mn_1.5O₄/graphite full cell were studied and the potential applications for MEC were demonstrated. Finally, we identify the benefits of MEC as a tool for future electrode/electrolyte interface or materials studies.

Section snippets

Experimental methods

Fig. 1(b) shows a schematic diagram of the MEC. The cell was made with a polypropylene body which contains L.E., electrodes, and current collectors (stainless steel rods at each side). A dense ceramic S.E., Li_{1 + x + y}Ti_2-xAl_xP_3-ySi_yO₁₂ (LTAP, OHARA, Inc.), with a thickness of 150 μm was placed between the L.E.s and completely sealed in order to prevent any electrolyte and any potential reduction or oxidation products to crossover while selectively transporting Li⁺ ions. Both regions of L.E. used 1 M

Results and discussion

Fig. 1 illustrates a schematic diagram and design of the MEC. In Fig. 1(a), traditional L.E.s have their highest occupied molecular orbital (HOMO) located above the electrochemical potential of the LiNi_0.5Mn_1.5O₄spinel positive electrode. They also have their lowest unoccupied molecular orbital (LUMO) located below the potential of graphite. As a result, both electrolyte oxidation and reduction will occur in the LiNi_0.5Mn_1.5O₄/L.E./graphite full-cell. However, the passivation layer (SEI) formed

Conclusion

The MEC successfully demonstrated its capability of blocking the migration of Mn^2 + ions and eliminating the effect of the “Mn dissolution” problem on the cell's electrochemical performances. This result instructs that incorporation of a S.E. in the Li-ion battery cell may solve the Mn dissolution problem. In addition, the MEC can provide additional benefits as a tool for future electrode/electrolyte interface studies with following examples; a) Since the MEC is capable of employing different

Acknowledgements

This work was supported by Funding Opportunities for Research Commercialization and Economic Success (FORCES) at Indiana University Purdue University Indianapolis (IUPUI).Authors would like to thank Bob R. Powell and Mark W. Verbrugge in Chemical & Materials Systems Laboratory in GM R&D for many helpful discussions.

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Short communicationMultilayer electrolyte cell: A new tool for identifying electrochemical performances of high voltage cathode materials

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental methods

Results and discussion

Conclusion

Acknowledgements

Electrochimica Acta

Solid State Ionics

Electrochimica Acta

Electrochimica Acta

Electrochimica Acta

Electrochimica Acta

Short communication
Multilayer electrolyte cell: A new tool for identifying electrochemical performances of high voltage cathode materials