Transcript Presentation

Center of Excellence POEMES, IEES (CLEPS), BULGARIAN
ACADEMY OF
e-School:
EMERGENCY VRLAB Methods and Techniques
for Testing and Research
B.Monahov
Institute of Electrochemistry and Energy Systems (IEES)
Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Center of Excellence POEMES, IEES (CLEPS), BULGARIAN
ACADEMY OF
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ABOUT THE E-SCHOOL
This e-School can be regarded as a specialized course from the group of
POEMES “cd” training courses, organized for young scientists and Ph. D.
students working in the field of Lead-acid batteries, but it can be also useful for
accumulation of general knowledge about methods for testing and microstructural investigations of batteries.
The trends in emergency batteries testing, monitoring and diagnostics are
marked. The capacity (rated, actual, expected), cycle life (expected for the
particular application profile), actual state of charge and state of health
(S.O.H.) are regarded as main battery parameters which should be controlled.
Two groups of testing methods can be distinguished: invasive (electrolyte
density determination and electrode potential measurements) and non-invasive
(open circuit and float voltage measurement, battery/cell temperature
monitoring, charge/discharge voltage measurement, DC current discharge, full
or partial charge-discharge and AC pulses or impedance).
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ABOUT THE E-SCHOOL
The presented material is outlining the most suitable techniques, which can
be used for the development of advanced methods for emergency batteries
testing and investigating. The possibilities for bridging between different
approaches are shown. Combined or single methods like in-situ XRD and
SEM/TEM, PRO, RAM, system integrated EIS devices and reference
electrode techniques are shown as promising tools for research and
development.
For convenience, the references concerning the presented information are
given directly on the corresponding page.
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Basic Abbreviations (I)
AFM – Atomic Force Microscopy
AGM – Absorption Glass Mat
CC – Current Control
CL – Corrosion Layer
DMA – Dynamic Mechanical Analysis
DSC – Differential Scanning Calorimetry
DTA – Differential Thermal Analysis
ED – Electron Diffraction
EMPA – Electron Microprobe Analysis
GC – Gas Control
HC – Gas Control
NAM – Negative Active Mass
ND – Neutron Diffraction
PAM – Positive Active Mass
PCL – Premature Capacity Loss
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Basic Abbreviations (II)
PCL 1 effect – a series of phenomena related to increased electric resistance
PCL 2 effect – a series of phenomena related to degradation of the positive active
material
PCL 3 effect – – a series of phenomena related to insufficient negative plate charge in
VRLAB
PM – Porometry
RT – Radioactive Tracing
SEM – Scanning Electron Microscopy
S.O.C. – State Of Charge (of a battery)
S.O.H. –State Of Health (of a battery)
SS – Specific Surface
STM – Scanning Tunneling Microscopy
TEM – Transmission Electron Microscopy
TGA – Thermogravimetric Analysis and DTGA
UPS – Uninterrupted Power Supply
VC – Voltage Control
XPS – X-ray Photoelectron Spectroscopy
XRD – X-ray Diffraction
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INTRODUCTION
1. The development of testing methods for the electric parameters of lead-acid
batteries during the first half of the last century, along with electrochemical
research techniques resulted in creation of a rich battery knowledge bank. The
structure of the active materials, however, was not known.
2. Structure research techniques (XRD, SEM, POR, RATM) used along with
sophisticated polarization methods like constant or modulated potential, CLSV,
RRDE etc. revealed the microstructure of the positive and negative active
masses and of the corrosion layer, their phase composition and crystal
structure, as well as the properties of the electrode systems formed on Pb in
H2SO4 and the mechanisms of action of the alloying additives.
3. Techniques for temperature and gas atmosphere control as well as for special
porometry were developed during the last three decades along with pulse
charge and impedance spectroscopy testing methods in order to study the
processes in VRLAB, to improve their technology and to detect instantly any
problems in them, and to make charging and maintenance of VRLAB easier
than of the other battery types.
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In this presentation various testing methods and techniques used to estimate
the capacity, cycle life, S.O.C. and S.O.H. of VRLA batteries in EES are
marked.
In addition to them, structure research methods that come to identify the
degradation phenomena and to address their causes and influence are
discussed .
The aim of the information introduced is:
•To make a brief introduction into the principles of these
techniques;
•To show typical results;
•To outline the main contributions to the understanding
of lead-acid batteries created using the above techniques.
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Aims of testing and research:
To answer the consumer’s general QUESTION:
When to replace the battery?
1. Testing: to estimate consumer related battery characteristics:
 Capacity (rated, actual, expected);
 Cycle life (expected for the particular application profile);
 Actual state of charge (S.O.C.);
 Actual state of health (S.O.H.).
2. Research: to solve producer related problems and save money:
 to reveal the mechanisms of the technological and chargedischarge processes, and of the degradation phenomena for the
particular battery;
 to explain the influence of battery the exploitation conditions .
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Battery testing methods
1. Invasive methods for on- and off-line testing.
(electrolyte samples are taken from the cell interior and analysed)
1.1. Electrolyte density determination - digital hydrometers,
concentration, s.g. and T of the electrolyte (not applicable for
VRLAB)
Fact estimation: S.O.C..
1.2. Electrode potential measurements. Reference electrodesPAM/NAM degradation.
Test methods detect battery facts but don’t explain their reasons.
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2. Non-invasive methods.
2.1. Open circuit and float voltage measurement – off- and on-line operation.
S.O.C./S.O.H.
2.2. Battery / cell temperature monitoring (IR) - on-line. Shorts, S.O.H., TRA.
2.3. Charge / discharge voltage measurement - on-line (requires additional info
about battery pre-history) . S.O.C./S.O.H.
2.4. DC current discharge (capacity estimation and conductivity problems
detection) - off-line. A load is connected to the battery - I, U, t. Capacity.
2.5. Full or partial charge-discharge for capacity estimation - off-line,
(Digatron/Firing circuits, Bitrode, Arbin Instruments, Solartron Analytical, ChenTech Electric Mfg., etc).
Battery connected to a PC-controlled stand. Expensive! All characteristics!
2.6. AC pulses or impedance spectroscopy - on-line, (Midtronics Inc., BatteryCorp Inc.).
A low amplitude periodic signal is passed through the battery,
the response is analyzed. S.O.C./S.O.H, shorts.
Test methods detect battery facts but don’t explain their reasons.
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Midtronics Inc., U.S.A. - conductance technology
Cell capacity vs.
conductance
 capacity of cells in good condition,
 degradation processes, shorts and open circuits,
 no load on the battery( no heat or sparks),
 powered directly by the battery under test.
recognized by IEEE as a standard for testing of
LAB with proven correlation to battery capacity.
Source: “Field and laboratory studies to assess the state of health of VRLA batteries: Part I – conductance /
capacity correlation studies”, D.O.Feder, T. Croda, K. Champlin and M. Hlavac, A paper presented to INTELEC
’92, Washington D.C., Oct. 4-8, 1992, Reprinted October 1992, http://www.midtronics.com/techpapers.html.
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Battery testing and monitoring
2
1 DC
AC
1
2
vent
full maintenance
LA battery
1.1. DC current
1.2. DC voltage
2.1. Electrolyte s.g.
2.2. Electrolyte T.
2.3. Ref. electrode.
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3
4
DC
cell
monitoring
and control
vent
maintenance free
LA battery
1.1. DC current
1.2. DC voltage
2.1. Electrolyte s.g.
2.2. Electrolyte T.
2.3. Ref. Electrode.
3. AC u/i – impedance (EIS)
4. Cell monitoring and control
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2
3
1
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AC
Blue
tooth
DC
line
valve
cooling
valve
monitoring
and control
VRLA battery
1.1. DC and pulse current
1.2. DC voltage
1.3. AC u/i – impedance (EIS)
2.1. No electrolyte s.g.
2.2. External cell ToC.
2.3. No ref. electrode.
2.4. Remote data /control
intelligent self
controlling cell
future battery
1. Optimal current
2. Optimal voltage
3. Optimal temperature
4. Optimal recombination control
4. Precise SOC control
5. Complex SOH diagnosis
6. Remaining C and cycles.
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Structure Research Techniques
(general)
The objects for the structure research techniques are either
extracted post mortem from real batteries, or artificially prepared
using one of the electrochemical polarisation methods – potential,
current or voltage control. The controlled parameter in the
particular method can be kept constant, swept linearly once or
cyclically or controlled in a pulse mode.
There are two groups of structure research methods. In the first
one the ambient conditions of the sample are controlled, while in
the second one special physical or physico-chemical techniques are
directly applied to the sample.
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Structure Research Techniques
(general)
Temperature and gas atmosphere control belong to the sample treatment techniques.
Most often thermostats are used to keep the temperature constant during a test.
Calorimetric equipment allows to measure and control the heat flows absorbed or
emitted by the sample, as well as to estimate the thermal parameters of the samples.
Temperature monitoring and mapping of cells/batteries provides in-situ information
about the electrochemical processes and about defects like shorts, dry-out etc.
The differential thermal analyses phase transitions and structure changes occurring in
very small amounts of samples on rising temperature can be identified very precisely.
The control or detection of the chemical composition, pressure or flow rate of the gas
inside the battery or around the sample during polarisation provides important
information about the structure of the active materials, as well as about the operation
of the so called oxygen recombination cycle in VRLAB.
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Structure Research Techniques
(general)
Pure structure research techniques are the optical (metallographic), SEM and
TEM, the recently developed STM and AFM.
The diffraction from crystals exposed to X-rays, electrons or neutrons is used
to investigate the properties of the crystalline battery compounds.
Special techniques are used to study the pore structure, size distribution,
volume and surface of the battery active materials and separators which are
extremely porous.
Radioactive isotopes are used to study the location and rate of the chargedischarge processes inside the battery.
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Electrochemical polarization methods
Nr.
Index
Method
Parameter
Specific
Constant – potentiostatic.
A
PC
Potential control Potential
Sweep – voltammetry (cyclic).
Pulse – potential pulse.
Constant – potentiostatic.
B
VC
Voltage control
Voltage
Sweep – voltammetry (cyclic).
Pulse – potential pulse, small pulse.
Constant – galvanostatic
C
CC
Current control
Current
Sweep – chronoamperometry.
Pulse – current pulse, small pulse
One or some of these methods are used along with sample treatment or
structure research ones to investigate battery components
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Sample treatment and structure research techniques
Nr.
Index
Method
Parameter
1.
TC
Thermo control
T
1.1. Thermostat
T, Q
1.2. Calorimetry
2.
GCD
Gas control and
detection
Specific branches and topics
T, t, x, y
1.3. T monitoring and thermal mapping
T, t, H, G
1.4. Differential thermal analyze
Chem.Comp.,
humidity, T
P
Flow
2.1. Gas atmosphere, Gas Chromatography etc.
2.2. Gas pressure
2.3. Gas flow
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Sample treatment and structure research techniques
Nr.
Index
Method
Parameter
1.
TC
Thermo control
T
T, Q
T, t, x, y
T, t, H
2.
GC
Gas control and
detection
CC, h, T
P
Flow
3.
M
Microscopy
Magnification
5.
D
PM
Diffraction
Porometry
SS
6.
R
Radiation
1.1. Thermostat
1.2. Calorymetry.
1.3. T monitoring and thermal mapping
1.4. Differential thermal analyze
2.1. Gas atmosphere, GC, RS.
2.2. Gas pressure
2.3. Gas flow
3.1. Optical microscopy (mm, OM)
keV, chem.comp,
3.2. SEM (nm, electron diffraction, EMPA, in situ)
keV, chem.comp,
3.3. TEM (nm, micro-micro diffraction, mapping)
F
4.
Specific branches and topics
3.4. AFM and STM (A)
2q
4.1. XRD (thermo, gas atmosphere, in situ)
2q
4.2. ND, ED
P, volume
5.1. Mercury porometry
P, flow
5.2. Capillary flow porometry
Volume
5.3. BET method (specific surface)
E, x, y,
8.1. Radioactive tracing (RT)
B. energy
8.2. XPS
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Combination of methods used to investigate
the components and the gas phase processes in VRLAB
1. Alloy structure: Opt.Micr., XRD, SEM, EMPA, DTA.
2. Active mass phase composition and structure: CC/CV, TC, XRD,
ND, ED, SEM, EMPA, TEM, DTA, GC, Rad.T, PM/SS,
3. Corrosion layer phase composition and structure: CC/CV , TC,
XRD, ED, SEM, EMPA, TEM, DTA, GC, Rad.T.
4. Separator structure and porosity: SEM, DTA, PM/SS.
5. Hydrogen and oxygen evolution: CC/CV, GC, XRD, SEM, TEM.
6. Closed oxygen recombination cycle: CC/CV , TC, GC, SEM, DTA,
PM/SS.