Rechargeable Batteries for Specknets

1
Rechargeable Batteries for Specknets

• Allan Paterson
• St Andrews Centre for Advanced Materials (STACAM)
• University of St Andrews
• ajp6_at_st-andrews.ac.uk

2
Plan

• Requirements and key power source issues
• Types of rechargeable batteries
• Li-ion batteries
• Commercial options
• Sanyo
• Thin Film Batteries
• New electrode materials
• Nano materials
• Lithium Manganese Nickel oxides
• Future Work

3
Requirements
Autonomous speck with renewable power source

• Require Specks to be small
  limit to energy storage
• Long periods between recharge high
  energy density
• Powerful supply for comms. sustain high
  currents

Secondary batteries

• Alternatives
• Radioactive Primary Batteries
• Efficiency too low. lots of energy stored, cant
  get at it.
• Capacitors and Thermoelectric Generators
• Relatively large devices.
• Solar Cells
• Still require energy storage when dark / cloudy
• Low power

4
Key Issues

• Energy densities
• Gravimetric (Wh/kg) ? lighter weight
• Volumetric (Wh/l) ? smaller size
• Power (W)
• Potential (V)
• Current (I)
• Recharge conditions and limits
• cell protection
• Fabrication of micro-batteries

Optimised Speck battery
Effects available capacity
5
Secondary Batteries

• Nickel Cadmium (Ni-Cd)
• 1.2V, 400 Cycles
• Inexpensive - Simple charging
• low energy density - Memory effect
• high self discharge (20 month)
• Toxic
• Nickel Metal Hydride (Ni-MH)
• 1.2V, 600 Cycles
• Simple to charge,
• High self discharge (30 month)
• reduced memory effect - Less-toxic
• Silver Zinc (AgZn)
• 1.5 V, 300 Cycles
• Low energy density - Very difficult to recharge
• Lithium Ion (Li-ion) based
• 3.5V, 2000 Cycles
• Higher energy density - No memory effect - Low
  self discharge
• Lower toxicity - More expensive - More complex
  charging
• Continuous current limited to 1.5C

Energy Densities
Smaller
Thin Film Li / Li-ion
Li-ion
Ni-Cd
Li-polymer
Ni-MH
Lighter
Pd-acid
6
Theoretical Energy Densities and Run Times
Estimated Energy Storage Available For Cubic
Specks

• Theoretical based on highest thin film and li-ion
  energy densities.
• Practical energy available determined by rate at
  which you discharge.
• Does not include packaging
• ? 1 1 1 mm cube difficult!

Theoretical
Practical
Packaged
7
Rocking chair Li-ion Battery
e-
e-
-

Li
charge
e-
e-
discharge
Li
LixC6 Graphite
Li conducting electrolyte
LiCoO2

• Electrode redox reactions on charge
• Cathode oxidation LiCoO2 ? Li1-xCoO2
  xLi xe-
• Anode reduction xLi xe- C6 ?
  LiC6

discharge is the opposite

8
Current Lithium Ion Systems

• A - Coin / Button Cells (Li-ion)
• LiMnO2 LiPF6 in EC/DEC organic electrolyte
  Graphite
• Rigid Aluminium packaging
• For clock / memory backup PDA type devices
• Available now, Sanyo, Varta, Seiko
• B - Pouch Cells (Li-Polymer Gel)
• LiCoO2 PEO or PVDF LiAsF6 or LiPF6 Graphite
  
• Soft or hard bodied complex form factors
• Large rectangular (20 ? 25mm) footprint but thin
  (2.5mm)
• Zero stack pressure no leaks, safer
• Common in Mobile Phone / Notebook / MP3 Players.
• C - All Solid State (Thin Film Li-ion)
• LiCoO2 LiPON solid electrolyte Li / Sn(O) /
  V2O5
• Highly crystalline electrodes, no
  binder/conductor
• Very thin battery (30µm)
• on rigid (0.4mm) or flexible (0.1mm) substrate
• No solvents/gasses/liquids to degrade or leak -
  Safer
• Sustain high continuous currents
• More tollerant of over charge/discharge ? No cell
  protection required

A
B
C
9
Sanyo Coin Cells
Sanyo Micro batteries ?-MnO2 Liquid
electrolyte Li-Al Alloy Model No
ML414 ML421 Voltage 3V 3V Dimensions
4.8 1.4 mm 4.8 2.1mm 555mm Speck
3 cells 2 cells (in parallel) Total Rated
Nominal Capacity 4mAh Max rated
Discharge Current 0.5mA Standard Charge
/ Discahrge Current 0.05mA ? Discharge
time of approx 5 to 6 hours for 1mW drain ?

• Electrochemical testing to establish
• Sustainable high currents, able to draw 1mW?
• Batteries actual capacity and resulting run time?
• Rate capability?
• Ease of recharge?
• Cyclability?

10
Sanyo - Electrochemistry
Recharge Conditions
Cyclability and Rate Capability
Constant Voltage Charge
Constant Voltage Charge
1mW
1mW
2mW
2mW
3mW

• At limits of size and max current for this
  system

• At manufacturers max rated recharge current
  time to recharge at least 1week.

11
Sanyo - Summary

• Extremely sensitive to recharge conditions
• Large depth of discharge significantly reduces
  cycle life
• 1 depth of discharge ? 20,000 cycles
• 10 depth of discharge ? 1,000 cycles
• 50 depth of discharge ? 100 cycles
• 100 depth of discharge ? 30 to 50 cycles
• 100 depth of discharge - non CC/CV fast
  recharge ? 20 cycles
• Higher power dramatically reduces run time
• 1mW ? 6 hrs
• 2mW ? 2 hrs
• 3mW ? ¼ hr
• Push as hard as can/need destroys the battery
• Alternative ? non Lithium Alloy at this size?

12
Thin Film

• All-solid-state device
• formed by sputtering
• Key Li2.9PO3.3N3.6
• ceramic electrolyte.
• Initial work by John Bates Oak Ridge Micro
  Energy Inc.
• Main option for specks smaller than 5 5 5 mm
• Prepared to make us some 5 5 mm footprint TF
  batteries
• Requires a design from us generation of mask
  set for 4.52 substrate
• Main issue is the location and dimensions of the
  contact patches
• Design rules recommendations from Christina for
  wire bonding to produce suitable schematic for
  cell fabrication shortly
• Conduct electrochemical performance evaluation
  and allow subsequent prototype device integration

13
Battery specification

• Size 0.3855mm
• Mostly packaging
• 55mm footprint
• ?4.54.5mm cathode
• 0.20cm2 ? 40µAh
• Fit 13 in parallel
• 500µAh 0.5mAh total
• Sustainable high charge/discharge rates
• At a power drain of 1mW then13 cells
• gives current density of 130µA/cm2
• No significant capacity reduction from IR loss at
  room temp.
• ? Total discharge time of battery stack 2
  hours

Anode Current Collector
Cathode Current Collector
Anode Cathode
Electrolyte
14
What for the Future?
Carbon nanotube

• Most improvement in energy storage and
  performance to be gained from RD of new and
  advanced electrodes.
• ? Materials chemistry challenge.

• Advanced Speck electrodes require
• Higher capacities ? Advanced Li-Mn-Ni-O
• Improved rate capability ? Nanomaterials

• Nanomaterials
• 1 Nanometre 1000millionth of a metre
• Simply by making materials small can have a
  profound influence on their properties.
• Inorganic oxide - Nanotubes and Nanowires.

15
TiO2-B Nano-tubes / wires

• Much interest in titanates, e.g. Li4Ti5O12
  Safe, low toxicity
• Voltage 1.5V, Capacity 160mAhg-1 (0.5 Li
  per Ti)
• ? Hunt for NEW titanates?

• TiO2-B Nano-tubes / wires
• TiO2-B most open of polymorph of TiO2
• High theoretical capacity
• Tubes/wires have 1D morphology
• Better particle contact ? Higher rate capability

Early reports of TiO2 tubes wrong ?
Na2-xHxTinO2n1xH2O
170?C hydrothermal H exchange, ?400?C
TiO2-B nanowires
High Yield
NaOH H2O TiO2-anatase
Armstrong, Armstrong, Canales, Bruce Angew.
Chem. 43, 2286 (2004)
16
TEM Images
TiO2-B Nanowires
TiO2-B Nanotubes
10nm
G. Armstrong, A. R. Armstrong, J. Canales and P.
G. Bruce Chem. Commun., 2005, 2454
17
TiO2-B Electrode Performance
The 1st Cycle
Rate Capability

• Intercalate Li up to Li0.98TiO2. (330mAhg-1) at
  low rates, 1.6V
• 2 that of anatase (150mAhg-1) or Li4Ti5O12
  (160mAhg-1)
• Excellent capacity retention and reversibility gt
  99.9 (wires)
• Able to sustain high charge / discharge rates
• 1st cycle irreversible capacity problem of
  conductivity?

18
New composite electrodes

• Encase active material in polymer gel
• Create porous electrode with all active
  material accessible by penetrating electrolyte ?
  increased conductivity.

Standard Composite Electrode - Active 75 -
Carbon Super-S 18 - Kynar Binder 7
1 to 2.5V LP30 Electrolyte
Optimised PEO Composite Electrode - Active
60 - Carbon Super-S 25 - PEO 15 -
Electrolyte Plasticizer 20 w/w of dry

• Highlights poor e- conductivity
• optimised PEO electrode does not address fully
  ? carbon coating?

19
Lithium Manganese Oxides

• Much interest in Mn based intercalation materials
  - LiMnO2 and LiMn2O4
• Cheap 1 cost of Co - Safe, low toxicity
• Potentially much higher capacities
• Almost ideal intercalation Electrode
  LiMn0.5Ni0.5O2
• Mn4 in octahedral sites stabilizes layered
  structure
• ½ Ni for electrochemistry Ni2 ? Ni4 2e-
• Manganese materials difficult to synthesise pure
  phases
• Very sensitive to synthesis conditions effects
  electrochemistry
• Difficult to make all Ni4 Susceptible to ionic
  mixing anti site defects

Li0.44MnO2
20
The Problem with Manganese

• Mn3 3d4 (High Spin) Jahn Teller Active

0 Mn3
50 Mn3
100 Mn3
?-MnO2
LiMn2O4
Li2Mn2O4
Undistorted cubic phase
Undistorted cubic phase
Co-operative Jahn-Teller distortion to tetragonal
symmetry

• To obtain a high capacity for any Li-Mn-O
  compound must be able to intercalate /
  deintercalate a large of Li
• ?1st order Jahn-Teller distortion ? 2 Phase ?
  Poor reversibility.

• Disproportionation type reaction above 4V
• 2Mn3(solid) ?Mn4(Solid) Mn2(solution) -
  active material dissolution

• Li2MnO3 composite to stabilise layered
  structure
• Potentially large improvement in performance
• from xLi2MnO31-xLiMn0.5Ni0.5O2 type
  materials Layered notation
  (LiLix/(2x)Mn(1x)/(2x)Ni(1-x)/(2x)O2)

21
Li-Mn-Ni-O System

• Possibly greatest initial interest
  0.3Li2MnO30.7LiMn0.5Ni0.5O2 - when discharged
  average Mn OS maintained above 3.5
• Large theoretical capacity as Li2MnO3 also
  electochem active - Li2MnO3 ? ?MnO2 Li2O (H
  exchange)

New composite
xLi2MnO3(1-x)LiMn0.5Ni0.5O2 composite or
LiLix/(2x)Mn(1x)/(2x)Ni(1-x)/(2x)O2
Layered LixMnyO2
LiMn2O4 Spinel
LiCoO2

• Potentially much higher capacities with
  optimised material 300mAhg-1

Li
(Mn / Ni)O6
22
Synthesis and Powder XRD results

• Mixed Hydroxide Co-precipitation
• Ni(NO3)2.6H2O Mn(NO3)2.4H2O Precursor

Dripped into LiOH soln. pH11 (3hrs)
Filter Wash
? 180oC 24hrs
? 900oC 10 hrs Then quench to room-temp.
? 80oC 24hrs
? 480oC 12 hrs Then re-grind
LiOH.H2O Grind in acetone
Ni1-xMnx(OH)2
LiLix/(2x)Mn(1x)/(2x)Ni(1-x)/(2x)O2 ?
xLi2MnO3?1-xLiMn0.5Ni0.5O2

• Powder X-ray diffraction
• - Successfully synthesis of
• 0.3Li2MnO30.7LiMn0.5NiO.5O2
• Fabricate electrodes
• Electrochemical testing

Prepared sample
Standard pattern
? 2?Fe Ka1
23
Summary and Further Work

• Sanyo Coin Cells
• Evaluated electrochemical performance
  difficult to recharge
• Issues with depth of discharge and max
  charge/discharge currents
• Source alternative li-ion / polymer battery
  systems of similar size
• ThinFilm Li-ion
• State of art all solid state thin battery
  technology we want thicker!
• Design of masks for fabrication and performance
  evaluation
• TiO2-B nanotubes and nanowires
• Excellent rate capability but large 1st cycle
  inefficiency
• Investigate conductivity issues possible carbon
  coating
• Li-Mn-Ni-O
• Successfully able to synthesise route to
  greatly increased capacity?
• Evaluate electrochemical performance of several
  compositions
• Investigate doping, e.g. Mg improved
  cyclability
• Reduce particle size - aid rate capability
• 3 D micro electrodes -another route to high
  sustainable currents