Effect of Li2CO3-coating on the performance of natural graphite in Li-ion battery

doi:10.1016/j.elecom.2003.09.014

Electrochemistry Communications

Volume 5, Issue 12, December 2003, Pages 979-982

https://doi.org/10.1016/j.elecom.2003.09.014 Get rights and content

Abstract

The effect of Li₂CO₃-coating on the performance of natural graphite in a Li-ion battery was studied. It is shown that Li₂CO₃-coating can effectively increase reversibility of the initial forming cycle of Li/graphite half-cell. More interestingly, the Li₂CO₃-coating significantly suppresses self-delithiation of the lithiated graphite, which enhances storage performance of the Li-ion battery. The Li₂CO₃–coated graphite also shows higher capacity retention after long-term cycling.

Introduction

Graphite has been used as an anode material in state-of-the-art Li-ion batteries due to high capacity (339 mAh/g) and low potential (0.1–0.3 V vs. Li⁺/Li) of its lithium intercalation compound (Li_xC₆, x=1). Reversible intercalation and deintercalation of Li⁺ ions with graphite are attributed to successful formation of a stable and protecting solid electrolyte interface (SEI) on the graphite surface, which is known to complete in initially few cycles [1], [2]. Previous studies have shown that formation of the SEI is greatly affected by electrolyte composition, morphology, and surface chemistry of graphite [3], [4]. For this reason, only a limited number of graphites have been found to be suitable for the anode of Li-ion batteries. To use natural graphite that is inexpensive and abundant, many researchers have currently focused on the surface modification of natural graphite [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. Both chemical and physical approaches have been attempted to modify natural graphite. Chemically, the graphite surface can be modified by mild oxidization, which has been verified to deactivate its catalytic effect on the electrochemical reduction of electrolyte solvents [5], [6]. Physically, morphology and chemistry of graphite surface can be modified by coating a protecting layer such as oxides [7], [8], metals [9], [10], disordered carbons [11], [12], polymers [13], [14], or simply by mechanical milling [15]. It is believed that the coatings preferably covered the active locations such as catalytic sites and particle edges, which therefore reduce solvent reduction and increase cycling stability.

On the other hand, Li₂CO₃ has been used as an electrolyte additive to improve reversibility and cyclability of graphite in a Li-ion battery [16], [17]. It was reported that the presence of Li₂CO₃ in electrolytes favors the formation of more compact and conductive SEI. As a result, initial irreversibility and its related gas generation were significantly reduced. Because Li₂CO₃ is rarely soluble in organic electrolyte, Xue proposed dispersing Li₂CO₃ powder throughout the electrodes and separator of Li-ion battery in the procedure of making them [18]. This approach was a significant improvement in the storage performance at elevated temperature. In this work, we will use Li₂CO₃ aqueous solution to modify natural graphite and discuss the effect of Li₂CO₃-coating on the performance of graphite in Li-ion battery.

Section snippets

Experimental

The electrolyte used was a 1.0 m LiBF₄ solution in a 1:1:3 (wt) mixture of propylene carbonate (PC), ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Water content of the electrolyte was determined to be 10–15 ppm by Karl–Fisher titration. Natural graphite (99%, 300 mesh, Alfa Aesar) was coated with Li₂CO₃ via the procedures described next. Graphite powder was added into a 0.5 wt% Li₂CO₃ aqueous solution and stirred for about 2 min to ensure that the powder was completely wetted.

Results and discussion

Previous studies have shown that using Li₂CO₃ as an electrolyte additive can help the formation of a more compact and conductive SEI, which further improves cycling stability of a Li-ion battery [16], [17]. This improvement is attributed to the participation of Li₂CO₃ into the SEI chemistry. However, such an improvement is limited since solubility of Li₂CO₃ in organic electrolytes is very low and the dissolved Li₂CO₃ cannot be fully utilized to form SEI. Therefore, in this work we use Li₂CO₃

Conclusions

Li₂CO₃-coating on graphite surface can effectively increase reversibility in the formation of SEI. It is speculated that the pre-coated Li₂CO₃ participates into components of the subsequently formed SEI. Due to very low solubility of Li₂CO₃ in organic electrolyte, the resulting SEI shows an improved stability at elevated temperatures. As a result, the Li₂CO₃-coated graphite shows lower self-delithiation in storage and better capacity retention in long-term cycling.

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Effect of Li2CO3-coating on the performance of natural graphite in Li-ion battery

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

J. Power Sources

Electrochem. Commun.

J. Power Sources

J. Power Sources

J. Power Sources

J. Power Sources

J. Power Sources

J. Power Sources

Electrochim. Acta

J. Power Sources

Electrochem. Solid-State Lett.

Effect of Li₂CO₃-coating on the performance of natural graphite in Li-ion battery