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Pitch as a carbon precursor for silicon alloy anode carbon coating and composite material for lithium ion battery applications

IP.com Disclosure Number: IPCOM000248353D
Publication Date: 2016-Nov-17
Document File: 8 page(s) / 364K

Publishing Venue

The IP.com Prior Art Database

Abstract

This paper describes using inexpensive coal tar pitch as a precursor to prepare coatings for silicon alloys and silicon alloy carbon composites. The final carbon coating could provide a better coating quality on the surface of the silicon alloy anode. The pitch coating could apparently reduce the electrochemical capacity fade and increase the cell cycling life for lithium ion battery applications.

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Pitch as a carbon precursor for silicon alloy anode carbon coating and composite material for lithium ion battery applications

This paper describes using inexpensive coal tar pitch as a precursor to prepare coatings for silicon alloys and silicon alloy carbon composites. The final carbon coating could provide a better coating quality on the surface of the silicon alloy anode. The pitch coating could apparently reduce the electrochemical capacity fade and increase the cell cycling life for lithium ion battery applications.

Background

Electrochemical energy storage has become a critical technology for a variety of applications, including grid storage, electric vehicles, and portable electronic devices. The lithium-ion battery (LIB) is an attractive energy storage device because of its relatively high energy density and good rate capability. To further increase the energy density for more demanding applications, however, new electrode materials with higher specific and volumetric capacity are required.

To meet the increasing demand for energy storage capability, novel electrode materials with higher capacity, low cost, and the ability to be produced at large scale are important. Alloy-type anodes (Si, Ge, Fe, Sn, Al, Sb, etc.) have much higher Li storage capacity than the intercalation-type graphite anode that is currently used in Li-ion batteries. Among all the alloy anodes, silicon alloys have the highest specific capacity. Some types of alloy anode materials have demonstrated an initial specific capacity of > 1000 mAh/g, which is 3-4 times of the capacity of graphite.

However, graphite anodes still dominate the marketplace due to the fact that alloy anodes have two major challenges that have prevented their widespread use. First, alloy anodes undergo significant volume expansion and contraction during Li insertion/extraction. This volume change can result in pulverization of the initial particle morphology and causes the loss of electrical contact between active materials and the electrode framework. Second, due to the low electrochemical potential of Li insertion/extraction (< 0.5 V vs Li+/Li), the anode surface becomes covered by a solid-electrolyte interphase (SEI) film, which forms due to the reductive decomposition of the organic electrolyte. In graphite anodes, a thin passivating SEI forms during the first few cycles, and its further formation is terminated due to the electronically insulating nature of the SEI. In alloy anodes, however, the SEI will rupture due to the volume change during cycling, causing the electrode surface to be cyclically exposed to the electrolyte. This results in continual formation of very thick SEI films, which causes the electrolyte to be continually consumed during cycling. The formation of SEI is further complicated by particle fracture, since fracture creates new active surfaces for SEI growth. The excessive growth of SEI causes low Coulombic efficiency, higher resistance to ionic transport, a...