2. Components of the battery:
• For battery manufacturing, there is aluminum copper foil on it due to cylindering process graphite as a anode
typically graphite(-), lithium based cathode( Commonly lithium-iron-phosphate (LFP) or lithium-nickel-
manganese-cobalt (NMC) also used one separator between the layer of Cathode, anode and
electrolyte( lithium salt) is used through which the ions are moving during charging and discharging.
3. • When the battery discharges, positively-charged lithium ions
move from the negative anode toward the positive cathode via
the electrolyte. This movement of ions causes a flow of
electrons in the other direction, which produces a current - and
electricity. Charging the battery works in reverse, with ions
flowing from the cathode to the anode.
4. Cause of Degradation:
• SEI:
During the first charging of the cycle a passivation film called SEI,builds
on graphite electrolyte interface.
When the charging process start, Li+ ion travel through the electrolyte
towards the graphite anode.
Some lithium ion reacts with degradation product of the electrolyte
and form insoluble solid parts that deposit on the anode.
Slow charging results in a densely packed SEI which prevents the
graphite structure from decomposition.
The SEI is stripping off the solvent molecules surrounding the LI+ ions.
5. • Actually the SEI prevents the anode lattice structure from exfoliation and allows
cycling of lithium batteries without major capacity fades.
• This layer traps lithium ions, restricting them from flowing between the anode and
cathode. This ultimately reduces the energy the battery can store and discharge.
2) Lithium plating: A further cause of degradation is lithium plating. This is where
metallic lithium forms on the surface of the anode when it can’t be absorbed. This
captures more lithium ions and can cause the SEI to grow, further reducing energy
capacity.
Excessive lithium plating can also cause the creation of dendrites. These excessive
build-ups of metallic lithium can cause physical damage to the battery itself and
even more catastrophic failures.
6. How does degradation change with use?
• To some extent, batteries are degrading all the time. However, it
gets worse every time the battery charges or discharges.
• Charging and discharging can be measured in cycles - one
cycle is equal to one full discharge of a battery's energy
capacity.
• This can either be done in one go (such as when wholesale
trading), or in smaller bursts across a longer period of time
(such as when providing frequency response).
• The more cycles a battery does, the more degraded the
battery becomes.
7. • It is common for the most severe degradation to occur at the
beginning of the system's use - with degradation of up to 10%
occurring in just the first year of use. The cell chemistry, the
materials used, and the manufacturing quality will determine the
amount of degradation.
8. • Do certain actions worsen degradation?
• Degradation occurs, to a small extent, passively - but worsens every time
the system is used. Because of the nature of degradation, however, some
actions will cause worse effects than others:
• High-power activities (i.e. actions at maximum power output).
• High depth of discharge activities (i.e. discharging from full to empty).
• Operation at extreme levels of state of charge.
• Operation at extreme temperatures.
• Avoiding these activities will reduce the impact of degradation on the
battery. However, it's common for safeguards to be in place to protect the
most damaging actions (e.g. limits to the state of charge that can be
reached).
9. • When the battery is working, these lithium ions move back and forth between two parts called the
cathode and the anode. But there's a challenge: the materials in the battery can react with the liquid
inside it, which is called the electrolyte. This reaction can cause the battery to wear out over time.
• To protect the battery, a special layer forms on the surface of the cathode and anode. This layer is
called the Solid Electrolyte Interface, or SEI for short. Think of it like a shield that sits between the
battery's materials and the liquid inside.
• The SEI layer is really important because it helps to control the flow of lithium ions. It lets the
lithium ions pass through, so the battery can work properly, but it blocks other stuff that could
damage the battery. It's like a filter that lets only the good stuff through.
• If the SEI layer is strong and well-formed, it helps the battery last longer and work better. But if it's
weak or damaged, it can cause problems like shorter battery life or even safety hazards.
• So, in simple terms, the SEI layer is like a protective barrier in a
rechargeable battery that helps it stay healthy and work well over
time.
10. • In the first year of a battery's life, the SEI layer forms and stabilizes during the initial charging and
discharging cycles. A well-formed and stable SEI layer is beneficial because it helps to minimize
unwanted reactions between the electrolyte and the electrode materials, reducing capacity loss and
ensuring efficient energy storage and release. Therefore, in the first year, a strong SEI layer
contributes to maintaining the battery's energy capacity relatively high.
• However, as the battery continues to be used over subsequent years, several factors can affect the
SEI layer and, consequently, the battery's energy capacity:
• SEI Degradation: Over time, the SEI layer can degrade due to repeated charging and discharging
cycles, exposure to high temperatures, or other stress factors. This degradation can lead to
increased impedance (resistance) within the battery, reducing its ability to store and deliver energy
efficiently.
• Electrode Degradation: Degradation of the electrode materials can also impact the SEI layer. As
the electrodes degrade, they may produce additional byproducts that interact with the electrolyte
and alter the SEI layer's properties.
11. • Dendrite Formation: If the SEI layer becomes damaged or unstable, it can lead to
the formation of dendrites—tiny, needle-like structures—that can penetrate the
separator between the electrodes, causing short circuits and capacity loss.
• Cycle Aging: Each charging and discharging cycle contributes to the aging of the
battery, gradually reducing its capacity over time. While a well-formed SEI layer
can help mitigate capacity loss, it cannot entirely prevent the natural aging
process.
• Therefore, while a strong SEI layer established in the first year can contribute to
maintaining relatively high energy capacity initially, its degradation over time,
along with other factors, can lead to a decline in capacity in the subsequent years
of the battery's lifespan. Regular maintenance, proper charging practices, and
operating within recommended temperature ranges can help slow down the
degradation of the SEI layer and extend the overall lifespan of the battery.
