Chapter 5

1. Cell Characterisation
The use of batteries in photovoltaic systems is distinct from batteries in other
types of batteries. The critical technological considerations for photovoltaic
systems arethat the battery has a long lifetime at virtually complete discharge
circumstances. Deep cycling and being kept at low charge levels for long
periods are not daily in rechargeablebattery applications. For batteries used to
startvehicles or other engines, the battery sees a significant; brief current
drain yet remains fully charged for most of its life. Similarly, uninterruptible
power supply batteries are kept charged for mostof their lives. The weight or
sizeof batteries in consumer gadgets is frequently the mostcritical
consideration. When choosing a battery, the followingaspects must be
taken into account.
1. Voltage
2. DischargeCurve
3. Capacity
4. Energy Density
5. Specific Energy Density
6. Power Density
7. Temperature Dependence
8. Service Life
9. Ability to Deep Discharge
10.Application Requirements
1. VOLTAGE
Eo values can be used to calculate the theoretical standard cell voltage
fromthe electrochemical series:
Eo (cathodic) (cell) = Eo (cathodic) − Eo (anodic)
This is the theoretical maximum voltage. The Nernst equation, which
considers the non-standard condition of the responding component,
changes the theoretical cell voltage. The Nernstian potential changes over
time due to use or self-discharge, which alters the activity (or
concentration) of the electro-active component in the cell. As a result, the
cell chemistry determines the nominal voltage at any given time. Due to
polarisation and battery resistancelosses (IRdrop). Itis determined by the
load currentand internal impedance of the cell. These variables are

2. influenced by electrode kinetics and consequently fluctuate with
temperature, chargestate, and cell age. The voltage that appears at the
terminal mustbe adequate for the desired use. The typical values of
voltage ranges less than 3.0 volts.
2. Discharge Curve
The dischargecurveis a graph of voltage versus capacity discharged as a
percentage. A flat dischargecurveis preferred because it ensures that the
voltage remains consistent while the battery drains.
3. Capacity
The amount of power involved in the electrochemical process determines
a battery's theoretical capacity. Q stands for the number of moles of
reaction, the number of electrons transferred per mole of response, and
Faraday's constant, wherex represents the number of moles of reaction, n
represents transferred per mole of reaction, and F represents Faraday's
constant.
Q = xnF
The capacity is often expressed in mass units rather than moles: Q =nFMr;
Mr= Molecular Mass. The capacity is expressed in ampere-hours per gram
(Ah/g).
The total battery capacity would never be realized since non-reactive
components such as binders and conducting particles, separators,
electrolytes, currentcollectors and substrates, and packaging contribute
significantly to the weight of the battery. A sloping potential profile above
0.15 V versus Na/Na+ accounts for around half of the capacity, whereas a
flat potential profile (a potential plateau) below 0.15 V accounts for the
other half versus Na/Na+, this anode was demonstrated to yield 300
mAh/g.
4. Energy Density
The energy density is the amountof energy extracted per unit volume of
the cell's weight.
5. Specific Energy Density

3. The specific energy density is the amount of energy extracted per unit of
cell weight. In one entire dischargecycle, it is the productof the specific
capacity and the operating voltage. Within a dischargecycle, both the
currentand the voltage may fluctuate. Therefore, the particular energy
obtained is computed by integrating the productof current and voltage
across time. The dischargeduration is proportionalto the maximum and
minimum voltage thresholds for a rechargeable battery. Itis determined
by the active materials' availability and avoiding an irreversiblestate.
6. Power Density
The power density is the amount of electricity extracted per kilogram of
cell weight (W/kg).
7. Temperature Dependence
According to kinetic theories, the reaction rate in the cell will be
temperature-dependent. Internalresistancechanges with temperature;
internal resistance is more prominent at low temperatures. Because ion
transportis hampered at shallow temperatures, the electrolyte may
freeze, resulting in a decreased voltage. The compounds may disintegrate
at very high temperatures, or enough energy may be available to trigger
undesirable, reversibleprocesses, lowering capacity. At lower
temperatures, the rate of voltage declines with increased discharge, and
the capacity will be faster.
8. Service Life
A rechargeable battery's cycle life is defined as the number of
charge/recharges cycles a secondary battery can do before its capacity
drops to 80% of its initial capacity. Typically, this is between 500 and 1200
cycles. The battery shelf life is the amount of time a battery may be stored
dormantbefore losing 80 percent of its capacity. The depletion of active
components by unwanted reactions within the cell causes the capacity to
decrease with time. Premature demise of batteries can also be caused by:
 Over-charging
 Over-discharging
 Circuit reversal
 It's drawing morecurrentthan it's supposed to.
 Experiencing severe temperatures

4.  Being subjected to physicaltrauma or vibrations
9. Ability toDeepDischarge
Because the depth of dischargeand battery life havea logarithmic
connection, a battery's life may be greatly extended if it is not totally
depleted; for example, a mobile phone battery can live 5-6 times longer if
it is only discharged 80% beforerecharging. For situations where this may
be required, special deep dischargebatteries are available.
10.ApplicationRequirements
The battery must be adequate for the application at hand. This implies it
must be able to generate the appropriatecurrentat the proper voltage. It
needs enough capacity, energy, and power. Itshould also not exceed the
application's needs by too much, sincethis will likely result in needless
expenditure; it should provide enough performance at the lowestpossible
cost.
The characteristics can further be differentiated by physical& electrochemical
characteristics. Physicalcharacteristics can be determined by multiple tests for
example; XRD, SEM, TGA, EDX, etc. Electrochemical characteristics can be
determined by CV (cyclic voltammetry). Following to the physical
characteristics
X-ray Diffraction (XRD)
X-ray diffraction experiments were performed to verify the crystalstructureof
as-synthesized materials. Thediffraction patterns of both cathode and anode
materials synthesized via solid-state methods have good agreement with the
reference patterns. X-ray diffraction analysis (XRD) is a materials science
technique for determining a material's crystallographic structure. XRD is a
technique that involves irradiating a material with incoming X-rays and then
measuring the intensities and scattering angles of the X-rays that exit the
substance. Identifying materials based on their diffraction patterns is one of
the mostcommon applications of XRD analysis. XRD provides information on
how the fundamental structurediffers from the ideal one due to internal
tensions and flaws, and phase identification. X-rays arewaves of
electromagnetic energy, whereas crystals areregular arrays of atoms. The
interaction of incident X-rays with the electrons of crystalatoms scatters

5. incident X-rays. Elastic scattering is the name for this phenomenon, and the
electron is the scatterer. The scatterers in a regular array create a systematic
collection of sphericalwaves. Thesewaves cancel each other out in most
directions due to destructiveinterference, but they contribute constructively
to a few suggestions, as Bragg's law indicates:
2dsinθ = nλ
Where d is the distance between diffracting planes, theta is the incidence
angle, n is an integer, and the beam's wavelength. The exact directions show
up as reflections in the diffraction pattern. As a resultof electromagnetic
waves impinging on a regular array of scatterers, X-ray diffraction patterns
emerge. Because their wavelength is frequently the sameorder of magnitude
as the separation, d, between the crystalsurfaces, X-rays areemployed to
create the diffraction pattern (1-100 angstroms). Theparticles of NaTi2(PO4)3
which was introduced during precursor preparations. Thepeaks and test
results can be understood in Fig.1
.
Figure 1. XRD pattern of NaTi2(PO4)3 prepared by solid-state reaction.
The fig 1 shows the XRD pattern of the synthesized NaTi2(PO4)3 composite
material. The NaTi2(PO4)3 has sharp diffraction peaks, and the XRD pattern
strictly agrees with the JCPDS No. 33-1296, showing the sample is a well-
crystallized spacegroup.

6. Thermogravimetric Analysis (TGA)
Under a controlled environment, thermogravimetric analysis analyses
weight variations in a substanceas a function of temperature. Some of its
main applications are the measurement of a material's thermal stability, filler
content in polymers, moisture and solvent content, and the percent
composition of components in a compound. Thermogravimetric analysis
(TGA) is performed using a thermogravimetric analyser device. While the
temperature of a sample is altered over time, a thermogravimetric analyser
continually measures mass. In thermogravimetric analysis, mass,
temperature, and time are considered base measurements, from which
numerous other measurements can be obtained. A thermogravimetric
analyser typically comprises a precision balance with a sample pan within a
furnace with programmable temperature control. To cause a thermal
reaction, the temperature is usually increased at a consistent pace (or, in
some cases, the temperature is regulated for a constant mass loss).
The thermal reaction can take place in a variety of environments, including
ambient air, vacuum, inert gas, oxidizing/reducing gases, corrosive gases,
carburizing gases, liquid vapors, or "self-generated atmosphere,"; and
pressures, such as high vacuum, high pressure, constant pressure, or a
controlled pressure.
The thermogravimetric data gathered during a thermal reaction is shown on
the y axis as mass or percentage of starting mass vs. temperature or time on
the x-axis. TGA curve is the name given to this graphic, commonly
smoothed. The DTG curve, the first derivative of the TGA curve, may be
plotted to find inflection points for in-depth interpretations and differential
thermal analysis. The TG curve of NaTi2(PO4)3 presents that the carbon
content of NaTi2(PO4)3 is about 1.1%
Figure 2. TGA profile of NaTi2(PO4)3 anode material.

7. Scanning ElectronMicroscopy(SEM)
The scanning electron microscope(SEM) generates various signals at the
surface of solid objects using a focused, high-energy electron beam. The
signals produced byelectron-sample interactions offer data on the sample's
properties, external morphology (texture), chemical composition, crystalline
structure, and orientation of the materials that make up the sample, among
other things. In most cases, data is gathered across a specific region of the
sample's surface, and a 2-dimensional picture is created to show spatial
changes in these qualities. Using traditional SEM methods, areas spanning in
width from 1 cm to 5 microns may be scanned in a scanning mode
(magnification ranging from 20X to approximately 30,000X, spatial
resolution of 50 to 100 nm). The SEM may also investigate individual point
locations on a substance; this approachis handy for discovering chemical
compositions (using EDS), crystalline structure, and crystal orientations
qualitatively or semi-quantitatively (EBSD). The SEM has a design and
function similar to the EPMA, and the two instruments have many
capabilities in common.
In an SEM, accelerated electrons carry kinetic energy, which is dissipated as
various signals caused by electron-sample interactions as the incoming
electrons decelerate in the solid sample. Secondary electrons, backscattered
electrons, diffracted backscattered electrons, photons, visible light, and heat
are examples of these signals. Secondary electrons and backscattered
electrons are often employed in imaging samples. Secondary electrons are
the greatest way to see the morphology and topography of materials. In
contrast, backscattered electrons are best for highlighting compositional
differences in multiphase samples (i.e., for rapid phase discrimination).
Collisions of inelastic incoming electrons with isolated electrons orbitals
(shells) of atoms in the sample create X-rays. Excited electrons create X-rays
with a specified wavelength when they return to a lower energy state. As a
result, each componentof a mineral "stimulated" by the electron beam has
distinct X-rays. SEM analysis is deemed "non-destructive." The x-rays
created by electron interactions do not cause the sample to lose volume,
allowing the same materials to be analysed several times. The following are
essential components of all SEMs:
 Electron Source("Gun”)
 Electron Lenses
 Sample Stage
 Detectors for all signals of interest
Minimum one detector is always present in an SEM, and most contain multiple
detectors. The detectors that an instrument may accepthave a significant impact
on its unique capabilities. The SEM is frequently used to provide high

8. resolution pictures of object forms (SEI) and to demonstrate spatial changes in
chemical compositions:
1. Acquiring elemental maps or chemical analyses with EDS
2. Phase discrimination based on mean atomic number (commonly related to
relative density) with BSE
3. Compositional maps are based on differences in trace element "activators"
(typically transition metal and Rare Earth elements) with CL
SEMs are also commonly used to determine phases using qualitative chemical
analyses and crystalline structure. The SEM may also be used to precisely
measurevery minute features and objects down to 50 nm in size.
Backscattered electron images (BSE) may be utilized to quickly distinguish
phases in multiphase mixtures. SEM observation reveals that NaTi2(PO4)3
particles are of differentsizes which are between 10mm to 100mm. The
following images shows the SEM images of the samples.
Figure3. SEM image of the synthesized NaTi2(PO4)3 atdifferent magnifications
(a) (b)10µm(c)20µm(d)30µm(e)50µm (f)100µm

9. Element Mapping / Energy DispersiveX-ray Analysis
An element map is a graphic representation of a sample's geographic
distribution of elements. Itis a 2D slice through the unknown sample
because it has been taken from a polished piece. Element maps are perfect
for exhibiting compositional zonation and displaying element distributions
in a textural context. An element map can be created using either an EDS or
an EDX system. Theimage is created by rastering the electron beam over a
target region. Consider an element map as a bitmap image based on
chemical elements pixel by pixel. The relative reaction of each component is
defined by how long the beam lingers on each location, and resolution is
governed by beam size(and, of course, the actual concentration).
Longer analyses can producemore differentiation but at the cost of time.
In many circumstances, EDS systems can get appropriateelement maps.
This is usually a speedier method, but it comes at the expense of resolution
and detection limitations.
Itis based on an interaction between an X-ray sourceand a sample. Its
characterization powers areprimarily to the fundamentalpremise that each
element has a unique atomic structure, resulting in a distinct collection of
peaks on its electromagnetic emission spectrum. Moseley's law predicts
peak locations with a level of precision much above the experimental
resolution of a standard EDX device.
A beam of electrons is directed into the material being investigated to
promote the production of specific X-rays from it. At rest, an atom in the
sample has ground state electrons bonded to the nucleus in distinct energy
levels called electron shells. The incident beam may excite an electron in an
inner shell, causing it to be ejected from the shell and leaving an electron-
hole in its place. The hole is subsequently filled with an electron from an
outer, higher-energy shell. The energy difference between the higher and
lower energy shells may be emitted as an X-ray. An energy-dispersive
spectrometer can determine the amountand energy of X-rays emitted by a
specimen. The material's elemental composition may be determined using
EDS because the X-ray energies indicate the energy differencebetween the
two shells and the atomic structureof the emitting element. The sample
contains ground state electrons in discreteenergy levels or electrons in
discrete energy levels; shells surround thenucleus. For further
investigation, the distribution of different elements in NaTi2(PO4)3 was
analysed by EDX analysis and elemental mapping. The figureindicates the
spatial distribution of elements like Na, Ti, P, and O, respectively. These
results show that Na, Ti, P, and O are uniformly distributed over the surface

10. of the NaTi2(PO4)3. Also, thedistribution of these elements is supported by
the peak position at a suitable energy level. In general, uncertainty is most
found in EDX data. Therefore, the deviation may occur in the percentage of
elements of the material.
QuantitativeResultsfor:Base(933)
Element
Line
Weight % Weight %
Error
Atom%
O K 20.19S --- 34.48
Na K 14.83 ± 0.59 17.63
P K 34.75 ± 0.54 30.65
P L --- --- ---
Ti K 30.23 ± 0.81 17.24
Ti L --- --- ---
Total 100.00 100.00
Figure 4. Elemental Mapping of the NaTi2(PO4)3 , indicating the spatial
distribution of Sodium(Na), Titanium(Ti), Phosphorus(P), Oxygen(O) along with
EDX analytical result.
Thus, fromXRD, TGA, SEM, EDX studies, it is proved beyond doubtthat Na is
embedded into the interlayer space of Ti2(PO4)3, forming a layered structureof
NaTi2(PO4)3. Thus, these are physicalcharacteristics

11. ELECTROCHEMICAL CHARACTERIZATION
The incident beam may excite an electron in an inner shell, causing it to be
ejected fromthe shell and leaving an electron-hole in its place. The hole is
subsequently filled with an electron from an outer, higher-energy shell. The
energy difference between the higher & lower energy shells may be
emitted as an X-ray. An energy-dispersivespectrometer can determine the
amount and energy of X-rays emitted by a specimen. The electrochemical
characterization is used to investigate the materials' electrochemical
behavior under various electrochemical circumstances. Thetwo-electrode,
three-electrode, and four-electrodesystems arethe three types of
electrode systems accessiblein an electrochemical cell. Any of these
electrode systems can be used to perform electrochemical
characterizations. A working electrode and a counter electrode make up an
electrochemical cell. The concentration of the analyte affects the potential
of the working electrode. The circuit is closed by the counter electrode. The
working electrode's potential should be determined concerning the counter
electrode, which serves as a reference electrode.
As a result, the counter electrode's potential should stay constant. The
state of the working electrode and the counter electrode, the ions of the
analyte in the electrolyte, and the current, charge, and voltage all affect the
electrochemical characterization of an electrochemical cell. All of these
factors will be linked to redox processes and will be responsiblefor changes
in the electrochemical characteristics of the materials.
Electrochemical characterization of the electrochemical studies of the
synthesized material is carried out in 1M,2M Na2SO4, 5MNaNO3, and 3M
NaOH electrolytes to understand the possible application of the materials
anode for aqueous rechargeable sodium-ion batteries.
Cyclic Voltammetry
CV (Cyclic Voltammetry) is an electrochemical method for determining the
currentin an electrochemical cell when the voltage exceeds that predicted
by the Nernst equation. CV is done by varying the voltage of a working
electrode and measuring the current.CV is the most basic electrochemical
material test. The currentis measured by brushing the potential back and
forth between the set boundaries (from positive to harmfulto positive). The
data gathered by CV can be utilized to understand moreabout the
electrochemical activity of the content. A cyclic voltammogram's graphical
analysis yields the redox peak, the material's reduction, and oxidation

12. peaks, forecasting the electrode's capacitive behavior. As a result, the
potential for oxidation and material reduction may be calculated.CV
receives a ramp signal as an input. A positive ramp (with a positive slope)
signal is supplied for the forward scan, whilethe voltage is switched after
the firsthalf-cycle. A negative ramp is provided for the second (next) half-
cycle, inverting the nature of the cyclic voltammogram. As the system
attempts to attain equilibrium through redoxreactions, it aspires to return
to the same place fromwhich it began. Itfollows a cyclic pattern that
provides information on the system's changes. Many essential conclusions
about the material and its characteristics (such as capacitive nature, etc.)
and the systembehavior may be drawn by appropriately evaluating the CV
curve(reversible, irreversible).
One potential cycle or numerous potential cycles can be used in the CV
experiment. The scan rate is the slopeof the ramp signal given in volts per
unit time. This scan rate can range from a few hundred volts per second to
a few fractions of a millivolt per second. The system's scan ratemay be
changed to understand the cell's electrochemistry better. As a result, the
scan rate significantly impacts the voltametric behavior of the evaluated
material. The oxidation and reduction peak currents and peak potentials
should shift depending on the scan rate. Also, if the peak current(faradaic
current) increases as the scan rate increases, the electrode material has a
strong rate capability and has a better pseudocapacitivecharacteristic [14].
Due to electroactive species at the electrode's (working electrode) surface,
a greater scan rate leads to moreredox reactions. However, due to the
considerabletime available for the products of the reduction or oxidation
to participate in a chemical process whoseeffects may not be electroactive,
a slower scan rate increases the risk of missing the peak (either forward or
reversescan peak). The Randles
Sevcik equation may be used to
compute the peak current in the CV.
ip = 2.69 x 10
5
n3/2
AC √AD
whereip is the peak current, n is the
number of electrons in the redox
reaction, A is the working electrode
area, C is the electroactive species
concentration at the electrode, n is
the scan rate, and D is the

13. electroactive species diffusion coefficient. All of these variables are
important in calculating the peak currentin CV. The electron transfer
coefficient (number of electrons transported), rate-limiting factor (a factor
that restricts the pace of the reaction), and rate constantof the response
may all be determined using CV. The difference between the two CV peak
potentials indicates the impacts of analyte diffusion rates. The anodic and
cathodic peak currents ratio may also determine if the system is reversible,
irreversible, or quasi reversible. If the aboveratio is 1, both the anodic and
cathodic peak currents arethe same, indicating that the system is
reversible. If the ratio mentioned aboveis not equal to 1, the system is said
to be quasireversible.
In contrast, the systemis said to be irreversibleif the oxidized or reduced
productis irreversible. Because the CV is taken in a scenario where the
solution is held undisturbed, the currentpeaks are essentially acquired;
otherwise, the peak current may be substituted by the limiting current. In
the caseof polymers, CV can readily anticipate the electrochemical
behavior of the polymer by utilizing the band gaps, electron affinities, and
work functions of the materials. As a result, CV investigates the compound's
chemical and electrochemical characteristics. The CV may also assistin
functionalizing materials by executing different redoxreactions utilizing
numerous scans and all of the benefits mentioned above.
Cyclic voltammetry and galvanostatic charge-dischargeexperiments were
used for this purpose. In figure5(a), wecan see the CV profile of 1M, 2M
Na2SO4 aqueous electrolyte scanned.CV profile of NaTi2(PO4)3 shows the
oxidation peak at 0.0653 mA and a reduction peak at -0.093mA.
The CV reveals a set of well-defined redoxpeaks in Na2SO4 solution, while
the peaks are quasireversibleand poorly identified in the case of NaNO3
and NaOH, as shown in figure.5(b). In figure.6(a) wecan see the CV profiles
at different scan rates of NaTi2(PO4)3 with Na2SO4 electrolyte between 0.1
mVs-1
to 0.5mVs-1
. Figure6(b) showsCV profiles of NaTi2(PO4)3 at higher
scan rates of 0.6mVs-1
to 1mVs-1
.

14. Figure.5(a)CV of NaTi2(PO4)3 in 2M Na2SO4 aqueous electrolyte (scan rate;
0.5 mVs-1
) (b) CV profile of NaTi2(PO4)3 different electrolyte.
Figure 6.CV of NaTi2(PO4)3 electrode recorded in 2M Na2SO4 aqueous
electrolyte at various scan rate (a) At lower scan (b) At higher scan rate.