D. Roy’s Group

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RESEARCH PROJECTS

Electrochemical Studies of Lithium Ion Battery Materials

 

Background

 

Applications of Li ion batteries vary widely from powering small devices to running hybrid electric vehicles and storing solar energy. Our research involves an array of electro-analytical techniques that are designed to characterize the detailed properties of novel materials for advanced lithium ion rechargeable batteries. We are interested in studying battery materials (focusing mostly on electrodes and electrolytes) that would meet the main desired goals of high-performance Li ion batteries: (i) Rapid recharge and pulse-power delivery; (ii) Improved operational and environmental safety; (iv) Wider temperature range of operation; (iii) High energy and power densities; (iv) Prolonged cycle-life; (v) High Coulombic Efficiency (ratio of charge-to-discharge capacities). Among the different aspects these materials that we plan to explore in the next few years, we are particularly interested in studying Li ion battery materials for solar energy storage.

 

Our present studies include metal oxide ceramics for cathodes, non-carbonaceous anodes, solid electrolytes and functional liquid electrolytes with tolerance for extreme temperature variations. Electrochemical studies of these battery materials are strategically coupled with morphological (scanning electron microscopy) and compositional (Energy Dispersive X-ray) analyses. The electrochemical performance tests include cyclability, galvanostatic charge/discharge profiles, coulometric titration, measurement of Li+ self diffusion in solid electrode and electrolyte composites, measurement of ionic and electronic conductivities in solid electrolytes, Ragone Plot (power density vs. energy density correlation)  construction, and temperature dependent performance profiles of half- as well as full-cells. This work has been supported through a CAT Development project of NYSTAR with NanoDynamics and Metamateria Partners.

   

 

Battery research facilities in our laboratory

 

Thin film electrode preparation: A Desk-top sputter coater (with all necessary attachments) is used in our laboratory to prepare current collectors/substrates for lithium ion battery anode and cathode films. Deposition of active material films is performed using standard techniques and the instruments (sonicators, stirrer/heater, vacuum ovens, etc.) necessary for this operation are available in our laboratory.

 

Spin-coater

Sputter-coater

 

Instruments used for thin-film electrode preparation.

 

 

Tube furnace used for the synthesis of materials for Li ion battery electrodes

A salt used for electrolytes, drying in a vacuum oven (top shelf). Cathode films deposited on Au current collectors are on the bottom shelf.

 

Battery cycling and charge-discharge profile analysis: Two fully automated state of the art galvanostat/potentiostat systems are used for these studies: Solartron Analytical Model 12528W Electrochemical System, and Princeton Applied Research VERASTAT3-400 potentiostat/galvanostat. Since cycling experiments often require several days of continuous data runs, both these electrochemical systems are interfaced with an online remote control system. Both the hardware and software of this latter system were developed in our laboratory. The setup allows for both half- and full-cell studies involving cyclability tests at different C-rates, Ragone Plot construction, slow scan voltammetry, as well as routine charge-discharge measurements.

 

 

Solartron Analytical Model 12528W Electrochemical System (1287A potentiostat /galvanostat + 1252A FRA) and PAR VERASTAT3-400 potentiostat/galvanostst with full EIS capability

 

 

Impedance characterization of electrode and electrolyte materials: Both our Solartron and VERSATAT systems are fully equipped for comprehensive sample analysis using electrochemical impedance spectroscopy (EIS). We also have the necessary software packages to perform complex nonlinear least square (CNLS) analysis of EIS data. In addition, we have a fully automated Fourier Transform Electrochemical Impedance Spectroscopy (FT-EIS) setup. The fast, home-built potentiostat used for this setup has a temporal resolution of 2 ms and the usable bandwidth is 1 mHz-1 MHz. Multiple spectra recorded for the same system within a short time provide reliable circuit models in CNLS analysis. Certain electrolytes tend to react with metal current collectors, often leading to corrosion of the latter. We study the fast kinetics of these reactions using FT-EIS and rotating disc electrodes composed of the metals of interest.  

 

 

Multi-frequency waveform for FT-EIS

(Lab-VIEW Virtual instrument)

http://people.clarkson.edu/~surop/

 

FT-EIS machine, shown with a rotator for a rotating disc electrode

 

 

 

RDE system used to study surface kinetics of electrolyte-induced corrosion of metal current collectors. RDE shifts limiting currents to higher overpotentials and facilitates Tafel analysis of corrosion parameters. RDE can also affect kinetically controlled currents of intermediate adsorbates.

 

Main experimental setup used for electrochemical characterization of battery materials.

 

Measurement of self diffusion (chemical diffusion) of Li+ in different electrode and electrolyte materials: This is an essential step for the evaluation of new battery materials, and a number of (stand alone as well as combined) techniques are used for this purpose. These include EIS (typically combined with galvanostatic charge-discharge), galvanostatic intermittent titration technique (GITT) and potentiostatic intermittent titration technique (PITT).

 

Humidity controlled chamber for battery material characterization: Electrolyte preparation, cell assembly and routine half-cell measurements are performed in a dry glove box (Terra Universal) with Dual-PurgeTM automatic humidity control. We have incorporated a rapid de-humidification component in this system using a number of series-connected column desiccators and a circulation pump. A number of specially designed feed-through connections (electrical, gas and liquid) to the dry box have been made for electrochemical measurements, Ar-purge, and cell temperature control.

 

External de-humidification unit for the glove-box

Relative humidity inside the glove box is monitored by the Nitrowatch unit and the automatic purge controller controls Ar flow in the box. 

 

Liquid electrolyte characterization through temperature dependent measurement of conductivity and viscosity: These measurements are performed using jacketed glass cells (in the Ar environment), and the temperature is controlled with a circulation bath (Brookfield Engineering model TC-602D), capable of accurately controlling temperatures between -20 and 150 oC. Electrolyte viscosities are measured using a Brookfield model LVDV-II+PCP cone-plate viscometer with a model CPE 41 cone (20 Hz shear rate). A Quadtek LCR Bridge (Model 1715 Digibridge) also is designated for electrolyte conductivity measurements.

 

 

 

Cone/plate system used with the viscometer for measuring (temperature dependent) viscosities of small samples of battery electrolytes

Circulator used to control the temperature of electrolytes in jacketed cells and cone/plate systems

 

 

 

Temperature controlled (Ar-filled) environment chamber used for probing temperature dependent properties of electrolyte materials.

 

 

 

Temperature controlled characterization studies of solid electrolytes and full battery cells: An environment chamber (TestEquity model 195A Half Cube) is interfaced with our Solartron EIS measurement platform. The chamber has a range of -40 to +130 oC with 256 step programmable control using the RS 232 interface and LabVIEWTM drivers. Specially designed plumbing lines for Ar-gas delivery and electrical connections are used with this setup, and the equipment has been interfaced with our online control system using LabVIEWTM software.

 

 

Viscometer setup used to measure temperature dependent viscosities of electrolytes for Li ion batteries

Sample preparation area

 

 

Eight-channel battery tester with home-built battery-holder box (for use in temperature controlled environment chamber)

 

 

Battery test station

 

Routine testing of battery cells: A computerized, eight-channel battery tester/analyzer is used for routine testing of Li ion battery cells. Charge-discharge rates and the voltage range can be varied at 0.1 – 10 mA up to 5V. Button cells and cylindrical cells are most commonly studied in our laboratory using this system.