Dinesh Mullangi Departmental seminar 12th August 2015

transcript

Porous Carbon-Germanium Nanoparticle Composites as electrode for Lithium Ion

Batteries

Dinesh Mullangi(Reg. No. : 20143296)

IISER Pune

• Introduction• Types of batteries• Applications of batteries• Anodic materials• Paper presentation• Summary

What is a battery?

https://www.google.co.in/search?q=battery

Primary batteries are non rechargeable Because their electrochemical reaction cannot be reversed. Ex. alkaline battery

Types of batteries

Secondary batteries are re-chargeableBecause their electrochemical reaction can be reversed. By applying a certain voltage to the battery in the opposite direction of the discharge. Ex. lithium ion batteries

Zn + 2 MnO2 + 2NH4Cl Zn(NH3)2Cl2 + Mn2O3 + H2O+electrical energy

Primary battery - Example

Secondary batteries - Rechargeable Li ion batteries

ANODECommercial anode materials: Hard Carbon, Graphite etc..

CATHODECommon cathode materials of LIBs are the transition metal oxides such as LiCoO2, LiMn2O4, LiNiO2, LiFePO4

ELECTROLYTE (solvent + salt)Role of electrolyte is ion conductor between cathode and anode. Ex: LiPF6 , LiBF4 in an Organic solvents .

Why Lithium/Lithium ions?

The mobile world depends on lithium ion batteries (LIBs), which provide portable

power for a variety of applications.

Due to their high energy density, low self-discharge, and long cycle life they form

ideal candidates for Secondary Batteries.

Li is lightest metal and has one of the highest standard reduction potentials (-3.0 V)

Theoretical specific capacity of Li is 3860 Ah/kg in comparison with 820 Ah/kg

for Zn and 260 Ah/kg for Pb

The first commercial lithium-ion battery was released by Sony in 1991

Lithium ion Secondary Batteries

Electrochemical Reactions in a LIB• Cathode

LiCoO2 Li1-xCoO2 + xLi+ + x e-cd

Cn + xLi+ + x e- CnLixcd

• Anode

• Overall

LiCoO2 + Cn Li1-xCoO2 + CnLixcd

AL CurrentCollector

Cu CurrentCollector

Electrolyte

LiMO2Graphite

SEI SEI

Lithium-Ion Battery Charge

CathodeAnode

AL CurrentCollector

Cu CurrentCollector

Electrolyte

LiMO2Graphite

SEI SEI

Lithium-Ion Battery Discharge

Anode Cathode

Applications of (LIBs)

SmartphonesDigital cameras

Robots

Electric vehicleshttps://www.google.co.in/search?q=battery

laptops

What is the requirement of a good anode material?

Requirements1) Large capability of Lithium adsorption2) High efficiency of charge/discharge3) Excellent cyclability 4) Low reactivity against electrolyte5) Fast reaction rate6) Low cost7) Environmental friendly and non-toxic

Anode materials

Graphite cannot meet the batteries demand for simultaneous high energy and

power densities.

Replacing the graphite anode with other Advanced Porous Materials having

higher reversible capacity and rate capabilities as well as long-term

cyclability is required.

Ragone plot showing Energy Density v/s Power Density for storage device

Commercially available LIBs are made of graphite anode, which has a specific capacity of 372 mA h g-1

This is the value to beat!

Benchmarking Li ion Battery based on graphitic electrodes

Large pore volume

High surface area

Shortened solid-phase lithium

diffusion distance

Full lithium ion accessibility

Efficient ionic and electronic transport between the

electrode-electrolyte interfaces

3D Mesoporous Structures

https://www.google.co.in/search?q=mof

Si has the highest specific capacity (4200 mA h g-1) But the poorest electrical conductivity and poor lithium diffusivity. Si anode can only cycle at slow rate.

Sn has good electrical conductivity due to its metallic nature

low lithium diffusion rate in Sn still limits them from being good electrode materials

In contrast, Ge exhibits good electrical conductivity

Good lithium diffusivity low charge/discharge potential Higher Energy density and Power densities

Thus, Ge could be an ideal candidate as anode material for LIBs

Among the lithium alloy-based anode materials

Nano Lett. 2014, 14, 1005−1010

Department of Materials Science and Engineering, Chonnam National University, South Korea

Energy Environ. Sci. 13th Aug 2015.10.1039/C5EE02183A

Duc Tung Ngo, Hang T. T. Le, Chanhoon Kim, Jae-Young Lee, John G. Fisher, Il-Doo Kim and Chan-Jin Park

20Fig. 1 Schematic diagram illustrating the procedure to synthesize 3D-Ge/C.

Powder X-Ray Diffraction (PXRD) patterns of 3D-Ge/C and diamond cubic Germanium

Raman scattering spectrum

Characterizations of 3D-Ge/C

Pore size = 20-100 nm The surface area = 124.9 m2/g Pore volume = 0.298 cm3/g

N2 adsorption isotherms at 77k and Inset shows the pore size distribution

Field Emission Scanning Electron Microscopy (FE-SEM)

(d) TEM image and SAED pattern (inset) (e) HR-TEM image and compositional line scanning profiles.

The d-spacing for (111) plane = 0.33 nm (220) Plane = 0.2 nm

(a) XPS general survey spectrum of 3D-Ge/C; high resolution XPS spectra of (b) Ge 3d, (c) C 1s, and (d) O 1s of 3D-Ge/C composite .

C 1s O 1s

Electrochemical studies Fast charging and slow discharging

Fast charging and fast discharging

High Efficiency and good Cyclability

Specific CapacityThe amount of charge that can be stored in a material per unit of volume or unit of mass.

Charge Rate(C)The current is applied or drained from the battery to complete charge or discharge it in one hour

Charge/discharge curves of the Ge/C electrode was measured at a rate of C/10 in the potential range 0.01–1.5 V

In the 1st cycle, The charge capacity is = 1604 mA h g-1

Discharge capacity was = 2286 mA h g-1

After 100th cycles, the reversible capacity was =1598 mA h g-1(99.6%)

Almost reached the theoretical capacity of Ge =1620 mA h g-1

Half cell studies

Charging

discharging

Cyclability test for 1-100 cycles Coulombic efficiency at a rate of C/10

Cyclic Voltammograms of 3D-Ge/C corresponding to the first three cycles

The Cathodic peaks are observed at 0.15, 0.37 and 0.51 V.

In the anodic sweep, the peaks are observed at 0.55 and 0.64 V.

• At 100C (26sec) ,The specific capacity of electrode = 1122 mA h g-1

• After 200 cycles, the reversible capacities were tested and found to be

almost 100% for different charging rates.

These results reveal the superior cyclability of the Ge/C electrode under

high charge rates

Potential profile at different charge rates and discharge rate was fixed at C/2

The Potential profile of Ge/C electrode at charge/discharge rates same .

Specific Capacity of the electrode = 697 mA h g-1 at charge/discharge rate is 50 C

Specific capacity = 1366 mA h g-1 at charged at 50C & discharged at C/2 rate

These results demonstrate that, the specific capacity of electrode was greatly

affected by the discharge process

Electrochemical impedance spectra

Impedance spectra at different lithiation states: (a) 20%, (b) 40%, (c) 60%, and (d) 80%

Charge potential vs time at different charge rates and discharge rate was fixed at C/2

Ultrahigh Charge Rates

Even at an ultrahigh charge rates high specific capacity could be achieved in just few seconds

Higher Energy density and Power densities

Cyclability and Coulmbic efficiency for 1000 cycles at a charge/discharge rates of 2C

long-term Cyclability and High Efficiency

Full cell is connected by using 3D-Ge/C anode and LiCoO2 cathode and capacities measured at a rate of C/10 and voltage profile (inset)

At 1st cycle , The charge and discharge capacities were 1901 and 1561 mA h g-1

Reversible capacity of the full cell (1491 mA h g-1) was slightly lower than half-cell

(1604 mAh g-1) at the same rate of C/10

Ultra-high rate cathode materials LiFe0.9P0.95O4-d, modified LiFePO4 and Li1.2Ni0.2Mn0.6O2 instead of LiCoO2

Full Cell studies

Fabricated the full cell LIB by using 3D-Ge/C anode and LiCoO2 cathode .

Up to 50-LED bulbs connected in parallel were successfully lit.

Summary

Successfully synthesized a Ge/C composite electrode with a 3D Nano architecture.

The 3D-Ge/C electrode exhibits excellent electrochemical performance: high

specific capacity, superior cyclability, and ultrahigh charge rate.

3D-Ge/C electrode offers high Energy density like batteries as well as a high Power

density like super capacitors.

The lithium diffusivity in 3D-Ge/C was ten fold higher than that of pure Ge .

3D-Ge/C electrode can be used in wide range of electrochemical devices. Such as

medical instruments, portable devices and then extended to electric vehicles.