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Hydrofluoroether Based Electrolytes for Silicon Alloy Anodes

IP.com Disclosure Number: IPCOM000249047D
Publication Date: 2017-Jan-30
Document File: 6 page(s) / 139K

Publishing Venue

The IP.com Prior Art Database

Abstract

This paper describes several prospective alloy anodes that provide a 100% increase in the composite electrode energy density compared to graphite coatings. In 18650 test cells using FEC-based carbonate electrolyte, a full cell energy increase of 15% to 20% against a standard NMC cathode has been demonstrated, and charge depleting cycling for 500+ cycles resulted in 60% capacity retention at a C/2 charge/discharge rate from 2.8V to 4.35V. Catastrophic failure still occurs under long term cycling due to electrolyte consumption. Non-carbonate electrolytes have the potential to eliminate this problem. In this paper, an electrolyte composition including at least a non-carbonate solvent was tailored for silicon alloy anodes. Combining these electrolytes with a silicon alloy anode and an NMC cathode will enable up to a 50% increase in the capacity retention after 200 cycles at room temperature. The new electrolyte composition includes (a) a solvent composition including a hydrofluoroether compound; (b) a solvent composition including a carbonate and/or an ester; (c) at least one lithium salt.

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Hydrofluoroether Based Electrolytes for Silicon Alloy Anodes

This paper describes several prospective alloy anodes that provide a 100% increase in the

composite electrode energy density compared to graphite coatings. In 18650 test cells using

FEC-based carbonate electrolyte, a full cell energy increase of 15% to 20% against a standard

NMC cathode has been demonstrated, and charge depleting cycling for 500+ cycles resulted in

60% capacity retention at a C/2 charge/discharge rate from 2.8V to 4.35V. Catastrophic failure

still occurs under long term cycling due to electrolyte consumption. Non-carbonate electrolytes

have the potential to eliminate this problem. In this paper, an electrolyte composition including at

least a non-carbonate solvent was tailored for silicon alloy anodes. Combining these electrolytes

with a silicon alloy anode and an NMC cathode will enable up to a 50% increase in the capacity

retention after 200 cycles at room temperature. The new electrolyte composition includes (a) a

solvent composition including a hydrofluoroether compound; (b) a solvent composition

including a carbonate and/or an ester; (c) at least one lithium salt.

Background

While commercial lithium-ion batteries (LIBs) perform satisfactorily for most home

electronics applications, currently available LIB technology does not satisfy some of the more

demanding performance goals for Hybrid Electric Vehicles (HEV) or Plug-in Hybrid Electric

Vehicles (PHEV), or Pure Electric Vehicles (EV). In particular, currently available LIB technology

does not meet the 10-15 year calendar life requirement set by the Partnership for a New Generation

of Vehicles (PNGV). At present, commercial vehicle batteries employ cells based on LiMO2 (M

= Mn, Ni, Co), LiMn2O4, and/or LiFePO4 cathode materials and graphite anode materials. In order

to achieve substantial increases in cell energy density, next generation anode candidates such as

silicon materials demonstrate very high specific capacities, with a theoretical limit of 4200 mAh/g

and state-of-the-art electrodes exhibiting capacities greater than 1000 mAh/g. Despite this promise,

silicon alloy anodes suffer from major disadvantages compared to graphite. For example,

carbonate-based electrolyte formulations do not form a stable SEI on silicon, resulting in high

irreversible capacity losses and poor cycle life. The volume expansion of Si based anode is another

issue, causing severe mechanical stress and electrical disconnection of particles.

While pure silicon materials have high energy density, they also show rapid fade in

commercially viable cell designs due to these issues. This paper describes several prospective alloy

anodes that provide a 100% increase in the composite electrode energy density compared to

graphite coatings. In 18650 test cells using FEC-based carbonate electrolyte, a full cell energy

increase of 15% to 20% against a standard NMC cathode has been realized, and charge depleting

cycling for 500+ cycles resulted in...