Non-aqueous Electrode Processing and Construction of Lithium-ion Coin Cells

Summary

Non-aqueous electrode processing is central to the construction of coin cells and the evaluation of new electrode chemistries for lithium-ion batteries. A step-by-step guide to the basic practices needed as an electrochemical engineer working with batteries in an academic experimental setting is furnished.

Abstract

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational analysis. Testing of lithium-ion batteries in an academic setting has taken on several forms, but at the most basic level lies the coin cell construction. In traditional LIB electrode preparation, a multi-phase slurry composed of active material, binder, and conductive additive is cast out onto a substrate. An electrode disc can then be punched from the dried sheet and used in the construction of a coin cell for electrochemical evaluation. Utilization of the potential of the active material in a battery is critically dependent on the microstructure of the electrode, as an appropriate distribution of the primary components are crucial to ensuring optimal electrical conductivity, porosity, and tortuosity, such that electrochemical and transport interaction is optimized. Processing steps ranging from the combination of dry powder, wet mixing, and drying can all critically affect multi-phase interactions that influence the microstructure formation. Electrochemical probing necessitates the construction of electrodes and coin cells with the utmost care and precision. This paper aims at providing a step-by-step guide of non-aqueous electrode processing and coin cell construction for lithium-ion batteries within an academic setting and with emphasis on deciphering the influence of drying and calendaring.

Introduction

Lithium-ion batteries represent a promising source to fulfill the ever increasing requirements of energy storage devices^1-4. Improvements in the capacity of LIBs would not only improve the effective range of electric vehicles^5,6, but also improve their cycle life by reducing the depth of discharge, which in turn increases the viability of LIBs for use in grid energy storage applications⁷.

Originally used for hearing aids in the 1970s⁸, coin cells today are commonly used in the development and evaluation of new and existing electrode materials. As one of the smallest form factors for batteries, the....

Protocol

Caution should be exercised when using any of the solvents, reagents, or dry powders utilized in this protocol. Read all MSDS sheets and take appropriate safety measures. Standard safety equipment includes gloves, safety glasses, and a lab coat.

1. Cathode Preparation

Note: The schematic overview of the cathode fabrication process is presented in Figure 1.

Results

A properly cast electrode sheet should appear uniform in surface appearance and properly adhere to the current collector. Typically flaking of the electrode sheet is caused by either poor etching of the substrate, or having to little NMP in the initial mixing stage. Alternatively, too much NMP can cause the sheet to display a higher degree of porosity, which is not desirable. Lastly, a third pattern can be observed on the electrode surface, where pooling appears to occur. Interactions wit.......

Discussion

The optimization of the wet mixing stages are crucial to the slurry viscosity and coating ability, which impacts the uniformity and adhesion of the electrode. Here a high-shear mixing method is utilized, where the solvent, additive, binder, and active material are mixed together utilizing the kinetic motions of the glass balls present in the vials. This mixing technique offers the benefit of much more rapid mixing times as compared to a magnetic stirrer method. Beyond this, this high shear mixing allows for more viscous .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
LiNiMNCoO2 (NMC, 1:1:1)	Targray	PLB-H1
CNERGY Super C-65	Timcal
Polyvinylidene Difluoride (PVDF)	Kynar	Flex 2801
1-Methyl-2-pyrrolidinone anhydrous, 99.5% NMP	Sigma-Aldrich	328634
1.0 M LiPF6 in EC/DEC (1:1 by vol)	BASF	50316366
Celgard 2500 Separator	MTI	EQ-bsf-0025-60C	25 μm thick; Polypropylene
Aluminum Foil	MTI	EQ-bcaf-15u-280
Lithium Ribbon	Sigma Aldrich	320080	0.75 mm thickness
2-Propanol, ACS reagent, ≥99.5%	Sigma Aldrich	190764
Acetone, ACS reagent, ≥99.5%	Sigma Aldrich	179124
Stainless Steel CR2032 Coin Cell Kit	Pred Materials		case, cap, and PP gasket
Stainless Steel Spacer	Pred Materials		15.5 mm diameter x 0.5 mm thickness
Stainless Steel Wave Spring	Pred Materials		15 mm diameter x 1.4 mm height
Analytical Scale	Ohaus	Adventurer AX
Agate Mortar and Pestle	VWR	89037-492	5 inch diameter
Tube Drive	IKA	3645000
20 ml Stirring Tube	IKA	3703000
Glass balls	McMaster-Carr	8996K25	6 mm diameter
Automatic Film Applicator	Elcometer	K4340M10-
Doctor Blade	Elcometer	K0003580M005
Die Set	Mayhew	66000
Vacuum Oven	MTI
Vacuum Pump	MTI
Laboratory Press	MTI	YLJ-12
Hydraulic Crimper	MTI	MSK-110
Glovebox	MBraun	LABstar
Battery Cycler	Arbin Instruments	BT2000
Potentiostat/Galvanostat/EIS	Biologic	VMP3