Elsevier

Solid State Ionics

Volume 225, 4 October 2012, Pages 354-358
Solid State Ionics

Electrochemical properties of all-solid-state batteries with ZrO2-coated LiNi1/3Mn1/3Co1/3O2 as cathode materials

https://doi.org/10.1016/j.ssi.2011.11.026Get rights and content

Abstract

All-solid-state lithium batteries were fabricated by use of LiNi1/3Mn1/3Co1/3O2 powders coated with ZrO2 as positive electrode materials and amorphous Li3PS4 as solid electrolytes. The ZrO2-coated powders were prepared by a sol–gel method associated with ultrasonic irradiation. The charge–discharge cycle performance of the all-solid-state cells was improved by use of the ZrO2-coated LiNi1/3Mn1/3Co1/3O2 powders. The ZrO2 coating was effective in suppressing an increasing of the interfacial resistance between the LiNi1/3Mn1/3Co1/3O2 electrode material and the sulfide based solid electrolyte, a-Li3PS4, during charge–discharge cycling. The battery with the ZrO2-coated LiNi1/3Mn1/3Co1/3O2 showed an initial discharge capacity of 115 mAh g 1 and good capacity retention even after 50 cycles at a current density of 0.1 mA cm 2 at room temperature.

Highlights

► ZrO2-coated LiNi1/3Mn1/3Co1/3O2 powders were prepared by a sol-gel method. ► All-solid state lithium battery was fabricated with the ZrO2-coated NMC powders. ► The battery showed discharge capacity of 115mAhg-1 at 0.1 mAcm-2 at room temperature. ► The battery also showed good capacity retention even after 50 cycles.

Introduction

All-solid-state lithium batteries using lithium-ion conducting solid electrolytes have been attracted much attention as highly safe batteries against conventional lithium ion batteries using organic solvents as electrolyte solution. The advantage of all-solid-state batteries is ascribed to nonflammable properties of the inorganic solid electrolytes [[1], [2], [3], [4]]. Although all-solid-state batteries have superior potential on the safety problems, there are some issues to be resolved for practical application. For instance, the operation under a high current density of more than several mA cm 2 is difficult and cycle performance of the batteries is gradually decreased with an increase in charge–discharge cycle numbers, when the all-solid-state batteries are made by use of transition metal oxides such as LiCoO2 which are widely used as positive electrode materials in the conventional lithium ion batteries with electrolyte solutions.

In the all-solid-state batteries, electrochemical reactions occur through the solid–solid interface between the electrode and solid electrolyte materials, and the interface governs the electrochemical properties. In order to improve the electrochemical properties, some studies have been conducted to form an effective electrode–electrolyte interface. Takada et al. have reported that interposed thin buffer layers such as LiNbO3 [5], [6], Li4Ti5O12 [7] between LiCoO2 cathode materials and the sulfide-based solid electrolytes are effective on the improvement of the electrochemical properties of LiCoO2 in all-solid-state batteries. Sakuda et al. [8], [9] have found that SiO2 coating on the LiCoO2 positive electrode materials works as a buffer to suppress the formation of high-resistance layers between the positive electrode materials and solid electrolytes. To our knowledge, however, those previous reports have been concentrated on the LiCoO2 cathode materials, and there are only a few reports on buffer-layer-coating effects on other cathode materials such as LiMn2O4, LiNi0.8Co0.15Al0.05O2, etc. [10], [11].

On the other hand, in the field of practical lithium ion battery with conventional electrolyte solutions, extensive studies have been carried out to improve the performance of the cathode active materials. Recently, manganese based layered compounds as positive electrode materials for lithium ion batteries are of great interest and are potential candidates to replace the commercial LiCoO2. Those include LiNi1/2Mn1/2O2 [12], LiNi1/3Mn1/3Co1/3O2 [[13], [14], [15]], and its derivations such as LiNixMnxCo1  2xO2 (0 < x < 1/3) [16], [17]. Among them, LiNi1/3Mn1/3Co1/3O2 has been studied extensively as promising positive electrode materials, because it exhibits much higher electrochemical capacity more than 200 mAh g 1 with enhanced safety. An alternate approach to improve electrochemical performance of the conventional lithium ion batteries is the surface modification of the positive electrode materials by coating their particles with some metal oxides [[18], [19], [20]]. Cho et al. [18] found that the thin-film coating ZrO2 on the particle surface of LiCoO2 had high fracture toughness which enabled to maintain structural stability of LiCoO2 by suppressing its non-uniform lattice-constant changes during Li de-intercalation, thereby preventing capacity fading during electrochemical cycling for the cells with conventional electrolyte solution.

We have considered that ZrO2 thin layer would work as a buffer layer between positive electrode materials and sulfide based solid electrolytes such as amorphous Li3PS4 in all-solid-state batteries. In this study, we have formed different amounts of ZrO2 coating on LiNi1/3Mn1/3Co1/3O2 particles by use of sol–gel methods associated with sonication, and investigated the effects of ZrO2 coating on electrochemical performance of the LiNi1/3Mn1/3Co1/3O2 cathode material in all-solid-state batteries with amorphous Li3PS4 solid electrolyte.

Section snippets

Experimental

The LiNi1/3Mn1/3Co1/3O2 powder provided by Nippon Chemical Industrial Co., Ltd. was used as a starting material and a reference sample. Coating layers of ZrO2 on the LiNi1/3Mn1/3Co1/3O2 powders were formed by use of a sol–gel method associated with ultrasonic irradiation. The ZrO2 coating sol was prepared from iso-propanol (99.5%, Wako), zirconium(IV) tetra propoxide (Zr(− OC3H7)4, Tokyo Kasei), ethyl acetoacetate (98%, Wako), and H2O in a molar ratio 170:1:1.5:6. The LiNi1/3Mn1/3Co1/3O2 powders

Structure and surface morphology of the ZrO2-coated LiNi1/3Mn1/3Co1/3O2 powder

The XRD patterns of the ZrO2-coated LiNi1/3Mn1/3Co1/3O2 powders are presented in Fig. 1. In the figure, the XRD pattern of the bare LiNi1/3Mn1/3Co1/3O2 powder is also shown for comparison. The main peaks can be indexed as a layered structure based on a hexagonal α-NaFeO2 structure (space group R3m). There is no diffraction peaks of crystalline ZrO2 in the XRD of the LiNi1/3Mn1/3Co1/3O2 powders coated with 0.7 and 1.4 mol% ZrO2. On the other hand, the sample coated with 3.5 mol% ZrO2 shows two

Conclusion

LiNi1/3Mn1/3Co1/3O2 particles coated with ZrO2 were prepared by the sol–gel method associated with ultrasonic radiation and were applied to the all-solid-state lithium cell using amorphous Li3PS4 solid electrolyte. The interfacial resistance between the 0.7 mol% ZrO2-coated LiNi1/3Mn1/3Co1/3O2 and the solid electrolyte was smaller than that between the bare LiNi1/3Mn1/3Co1/3O2 and the solid electrolyte. The charge–discharge performance of the solid-state cells was improved by the ZrO2 coating

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