high-performance flexible energy storage and harvesting system for wearable electronics - commercial energy storage systems

This paper reports the design and operation of a flexible power supply integrated with lithium-ion batteries and amorphous silicon solar modules, which is optimized to power wearable health monitoring devices.
The battery consists of a printed anode and cathode layer based on graphite and lithium cobalt oxide, respectively, on a thin flexible current collector.
The energy density is 6.
98 mmwh/cm 2, and maintain a capacity of 90% at 3C discharge rate, and maintain a capacity of about 99% at 100 charge/discharge cycles and 600 mechanical bending cycles.
Solar modules with appropriate voltage and size are used to charge the battery in sunny and indoor lighting conditions, and the addition of solar modules is displayed while powering the load, extended battery life between charging cycles.
In addition, we show that the average load current can match the solar module current by selecting the appropriate load duty cycle, and the battery can maintain a constant charging state.
Finally, the battery is used to power the pulse oximeter, proving its effectiveness as a power supply for Wearable Medical Devices.
Lithium cobalt oxide (LCO)
Synthetic graphite is used as the active material of cathode and anode respectively.
Mixture with a cathode slurry of 80 wt % LCO (MTI Corp. ), 7. Graphite (5 wt %)SFG 6L, TIMCAL), 2.
5 wt % carbon black (
TIMCAL Super C65)
And 10 wt % Poly difluoride (
Kureha Corp. )in N-methyl-2-pyrrolidene (
NMP of Sigma Aldrich)as the solvent.
A mixture of 90 wt % synthetic graphite with an anode slurry (MTI Corp. ), 4.
5 wt % carbon black (
TIMCAL Super C65)and 5. 5u2009wt% PSBR (
Targray Technology)
It is solvent with deionized water.
Stir overnight using a vortex mixer to homogenize the slurry.
Printing cathode and anode paste on stainless steel (SS, 12. 5u2009μm, Grainger)and nickel (
10 μm, Targray Technology)
Use the doctor blade to foil at a speed of 15 mm/s respectively.
The electrode heats up in an oven at 80 °c for two hours.
The thickness of LCO and graphite electrodes is 75 and 65 μm, respectively, after pressing them to 30% pores.
The surface load of cathode and anode is 17, respectively. 85 and 7.
17 cm, respectively.
The electrode is cut into a size of 2x2 (25. 81u2009cm).
The theoretical capacity of cathode and anode is 53, respectively. 8u2009mAh (2. 09u2009mAh/cm)and 58. 23u2009mAh (2. 26u2009mAh/cm)Respectively (
The theoretical ratios of LCO and graphite are 145 and 50 mah/g, respectively).
The cathode is the limit electrode in the battery.
The ratio of anode to cathode theoretical capacity is 1. 08.
Before installing the battery pack in the glove box, heat the electrode in the vacuum oven connected to the glove box for 12 hours to remove the residual solvent in the electrode.
Prepare the complete battery by stacking the anode (
Graphite on nickel foil)and cathode (LCO on SS foil)
Separator based on polypropylene (20u2009μm, Celgard).
Soak the stack with an electrolyte solution of 1 M LiPF in EC/December (1:1)(MTI Corp. ).
Nickel and aluminum sheets are used for electrical contact with the current collector of the anode and cathode, respectively.
Stacked hot sealed inside aluminum
Laminated bag (
Sigma Aldrich polyethylene/aluminum/polypropylene).
After sealing, the battery is allowed to rest for a day to ensure that the electrode is fully moist.
The battery is chemically cycled using a battery analyzer (MTI Corp. ).
During the formation of the cycle, the battery cycles at a C/20 rate (2.
69 YMMA, theoretical capacity based on cathode)between 4. 2 and 3.
Three cycles 0 v.
Due to the consumption of lithium ion during the formation of the solid electrolyte interface, the Cullen efficiency of the first cycle is about 85-88% (SEI)
Layer, but increased to more than 99.
9% the end of three cycles.
The capacity of the battery after the formation of the cycle is 47. 5u2009mAh. The C-
The battery rate for further electrochemical experiments is based on the discharge capacity obtained at the end of the third formation cycle, I . E. e. 1Cu2009=u200947. 5u2009mA.
Electrical impedance spectrum (EIS)
Scanning with a constant potential meter (Ivium)
In the frequency range of 10 to 0.
1 hz with an amplitude of 10 mv.
Scanning electron microscope (SEM) Microscopic images are used in desktop scanning electron microscopy (Hitachi).
The battery is bent by a plastic pipe track with a bending radius of 3 to 1 inch.
Flexible amorphous silicon photovoltaic module (Powerfilm MPT3. 6–75)
Used to charge the battery.
Photovoltaic Module current-
Get voltage features and battery charging features using Keithley 2400 power supply-
Represents the instrument under indoor and outdoor lighting conditions.
"Outdoor" conditions, air quality (AM)1.
5 The Global Illumination with a irradiance of 100 mw/cm was simulated with Oriel Sol1A solar simulator.
Two indoor conditions were compared and 13 w compact fluorescent bulbs were used at two different distances from the PV module 5 cm and 16 cm.
The irradiance is about 4. 8 and 0.
The two distances measured using photodiodes are 9 mw/cm (Hamamatsu 66R)
And Spectrometer (
CCS labs CCS 200).
Flexible power supply integrating photovoltaic modules, batteries and barrier diodes (
Schottky diode ON Semiconductor
It was also built.
Electrical connections are made using a combination of copper foil, conductive epoxy and welding.
In order to characterize the behavior of the battery that connects the solar module and the load at the same time, Giri source-
The meter is configured to repeat the drawing of 20 ma within the specified time, followed by the drawing of 1 ma within the specified time, simulating the pulse oximeter in the "on" and "off" states
The PV module is exposed to any of these 4. 8 or 0.
As before, the light using a compact fluorescent bulb is 9 mw/cm. The source-
The meter monitors the load current and voltage throughout the process.
A pulse oximeter based on ti Instruments is used for data collection and processing of Oximeter.
A photo (PPG)
Get the signal from the volunteer's index finger in red (632u2009nm)and infrared (940u2009nm)light-
LEDs (LEDs)
Silicon Photodiodes (PD)at 1u2009kHz.
The PD current signal is then filtered, amplified, and converted to a voltage signal. A 10-
Bit analog to digital converter (ADC)
Used to digitize analog signals.
Finally, the universal asynchronous receiver/transmitter (UART)
Use the protocol to send processed data to the computer for visualization.
The photoelectric probe, the LED driver, the PD reading circuit and the micro-controller board are powered by flexible batteries.