Degeneration of a Rechargeable Battery

A lithium (Li) battery consists of a negative electrode, which is called the anode, and a positive electrode called the cathode. In between the anode and cathode is the electrolyte.
The ions (charged atoms) flow through the electrolyte to create its power.
The cathode is usually made of a metallic compound, for example lithium cobalt oxide or lithium manganese oxide. Whatever is used must be able to release Li ions easily.
The anode is made of lithium bound to a materials such as graphite or other carbons.
The electrolyte is made of a material similar to the cathode in order for the ions to flow.
When the battery is supplying energy, the Li ions from the cathode consisting of a metallic compound flow through the electrolyte and into the anode.
The Li ions have a positive charge. While the Li ions flow, electrons will flow through the load from the anode to the cathode, but not through the electrolyte.
The electrolyte only allows ions to diffuse through it.
The battery charge / discharge process is operated by the repetitive flow movement of ions between electrodes. By the process of repetition and the electrode oxidation, the battery performance, charging capacity and battery life are progressively reduced.

Charging
 
Discharging
 • Battery is connected to a charge (power source).
 • Positive electrode (cathode) is oxidized.
 • Electrons flow through the outer circuit to negative electrode.
 • Li+ ions float through the electrolyte to negative electrode.
 • Electric circuit is closed.
  Li+ ions are incorporated into the negative electrode.
 • Battery is connected to a load (resistance).
 • Negative electrode (anode) is oxidized.
 • Electrons flow through the resistance to positive electrode.
 • Li+ ions float through the electrolyte to positive electrode.
 • Electric circuit is closed.
 • Li+ ions are incorporated into the positive electrode

Crystalline Formation
After several charging cycles, batteries progressively lose their performance because the electrical elements efficiency decreases and the internal chemical transfers are reduced by the effects of crystalline formation caused by the oxidation (inter-metallic compound) which create extra resistance that cause the degeneration of a battery.
Battery Separator
The separator, a metal that is shared by both chemistries, is responsible for this crystalline formation, creating crystals with sharp corners that may pierce the separator, which can lead
to increased self-discharge or an electrical short. The crystals grow and drastically reduce the surface area. The result is a voltage depression, which leads to a loss of capacity. In advanced stages, the sharp edges of the crystals may grow through the separator, causing high self-discharge or an electrical short.
The ion's flow is no longer operating correctly, thereby reducing the battery life.
Mechanical Stress
The heat due to charging-discharging cycles and the movement and accumulation of ions to the electrodes causes a mechanical alteration in volume (expansion + contraction) for a approximate value of 7-9% of the total volume. Incorporation and removal of Li-ions (approx. 0,12 nm) at electrodes causes the alteration in volume (expansion + contraction).
The mechanical stress causes the partial decomposition of the electrodes and metal particles float within the electrolyte.
These particles cannot be ionized by normal battery function anymore and are lost as charge carriers.

In addition to the natural battery deterioration, others external factor can affect the performance. For example, the battery is also damaged and its performance reduced by the use of cigarette-lighter adaptors, which do not properly regulate the incoming current.

 Results: A shorter battery life and life span, a lower charging capacity and a longer charging time

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