Forward by Ken Myers
The article is somewhat technical but quite "readable".
The sections about Cell Failures and Their Causes, Signs of Damage and How to Provide Long Life to Cells/Packs are found at the end of the article and should be noted carefully. The reader may wish to start with those three sections and then return to the beginning to see how and WHY the statements were formulated.
Read the last three sections now

Special thanks to Dave Stacer, friend and flying buddy, for his assistance in proofing and formatting this document.

What Flows in the Cell?

The Periodic Table shows that Lithium, after hydrogen and helium, is the lightest element. Lithium is an alkali metal with three protons in the nucleus and three electrons in the outer shell.
A Lithium-ion has three protons in the nucleus, but only TWO electrons in the outer shell. That makes it a positively charged ion.

Charging

The cell has a positive (+) Aluminum (Al) terminal and negative (-) Copper (Cu) terminal.
The Cathode consists of Lithium cobalt oxide, Lithium manganese oxide, or Lithium iron phosphate, among others.
The Cathode carrier is made of aluminum.
Typical thicknesses are shown in the diagram for the cathode, separator and anode.
The Anode consists of Carbon (graphite) and the carrier is made of copper or (less often) nickel.

At 1 amp of current for every second there flows 6.2 x 10¹⁸ positive Lithium Ions through the cell.

Voltage Curve

The graph illustrates the voltage curve theory. There are lines for the Cathode (Half-cell 1), Total cell (Gesamte Zelle) = (Half-cell 1 and Half-cell 2) and Anode (Half-cell 2).

The total life depends on cycle aging caused by damage in the cell by charging and discharging and storage-aging causing damage in the cell.
aging^total = aging^cycle + aging^storage

The effects of aging are a decrease in capacity, increase in internal resistance, a decrease in current capability, and a decrease in the maximum possible charging current.
Aging occurs nonlinearly. After a certain degree of cell damage, it occurs more quickly (see section "Cell Chemistry" for details)

Current and Ion Flow

The heat development of the cell during charging and discharge is composed of two elements:
Irreversible heat
This is due to the ohmic resistance and electrochemical processes during overcharging and/or over discharging.
Reversible heat
This is caused by the electrochemical processes during the normal charge and discharge cycle.

For high-current applications, the irreversible heat generation dominates, especially during discharge.
For a long cycle life, it is important to operate the cell in its optimum working range. Too low of a temperature causes damage, as well as too high of a temperature.

Thermal Runaway

Intercalation
Intercalation (from the Latin intercalare = insert), in the chemical sense, is defined as the incorporation of molecules or ions, but rarely atoms, in chemical compounds, which do not substantially alter their structure during the storage process.

The cell performance depends on:
Current:
The Ion transport capacity
"How many ions can flow per unit of time?"
The more ions that can flow per unit of time yields a High Current Cell.
Limited by:
Surface
Interfaces (Transitions / Layers) yields Terminals
Temperature

Capacity:
Ion release and ion absorption capacity
"How many ions, that the cathode emits during charging, can fit in the anode?"
Yields a high capacity cell

Anode Chemistry

The Importance of Transition Zones or Interfaces

Anode Cell Chemistry

The SEI-Layer provides protection and stabilization of the anode. Without an SEI layer there is no cycle stability.
Unfortunately the SEI layer results in an increase in internal resistance. The thicker the layer, the higher the resistance.
The SEI Layer also causes a loss of free Lithium.
The thicker the layer, the less remaining capacity there is because of decreased lithium transportability.
The thicker the layer, the more sensitive it is to plating deposits.

The SEI layer is basically constructed in the preparation of the cell. Any cell which is 'new' has already experienced at least one preparation cycle.
The SEI layer grows during the life of the cell. The more degradation products that are caused in the cell, the thicker it is. High pressure and temperature accelerate this degradation.

The deposition of metallic lithium ions at the anode, when charging, is called plating.
Dichtegradient means density gradient.

Plating occurs when 'the anode wants more Li⁺ ions in' than can be accommodated with the transportation capacity available.
This happens when charging, not during discharge.
When the cell reaches maximum capacity, overload can occur to the already fully replenished anode (greater than 4.2V in normal cells).
The transport capacity can be reached by using too high of a charging current, charging at too low of a temperature and the state of the cell's aging, caused by deposits of the oxidation products of the electrolyte and SEI Layer thickness.

More on Thermal Runaway

The temperature rise to 'Onset' can also occur slowly (minutes to hours). Once this is achieved, however, the heating occurs faster locally.
The warming 'Onset' gets its energy from the charging of the cell. In a cool storage environment, a higher heat generation is necessary. This also assumes the necessary size of the triggering 'Shorts' and Bigger 'Shorts' are rare and reach a certain size only by mechanical damage.
From outside, these processes in the cell are not easy to detect.
For a small cell capacity this damage can be detected from a slightly elevated self-discharge. For larger capacities, however, this indication is weaker. In such cells, at less than 3.3V, the problematic cells can only be detected in test runs by repeated slow charge amd discharge in the low cell voltage range. On the basis of small, impulsive changes the charging current can be detected.
Micro-shorts cannot easily be ruled out, so you have to minimize the likelihood that they might trigger runaways.

A cell must have sufficient energy stored for a runaway. The higher the SOC, the more likely it is.
High ambient temperature favours a runaway.
Advice: It is best to keep the pack cool, 20°C (68°F) or less, and store at a low state of charge (SOC).

Factors for the formation of plating include high charging current, low temperatures (while discharging), old or overloaded cells with a thick SEI layer, flaws from manufacturing defects or damage, or too high of a discharge current. (See explanation of the Cathode.)
Advice: Never cold discharge cells at a high C-rate load.

Chemistry of the Cathode

When charging, the positive lithium ions move from the cathode to the anode.
Upon discharge, the cathode accepts positive lithium ions.
As with the anode, there is a transition zone ("interface") to the electrolyte.
In contrast to the anode, there is no "SEI layer", but instead, reaction products diffuse into the electrolyte.

Chemistry of the Electrolyte

Additives are used to:
Improve the SEI formation
Protect the cathode and electrolyte (Oxidation inhibition and Li Retention)
Provide LiPF₆ temperature stabilization
Provide overload protection ("Redox Shuttle")
Provide fire prevention ("Fire-Retardant")
Provide a wetting agent (Manufacturing, wetting of the electrode)
Provide corrosion protection for the Aluminium
In 2014 there were about 3 to 5 additives used in each cell.

Failures Caused by Voltage Errors

If the voltage is too high, greater than 4.25V, the Cathode has stress caused by extreme delithiation, the Anode suffers from lithium plating yielding Lithium dendrite formation and the Electrolyte decays due to the oxidation processes at the cathode.

If the voltage is too low, less than 2V, the Cathode has stress due to high delithiation and Oxygen is released, the Copper carrier dissolves releasing oxygen and producing copper (Cu) dendrites on the Anode.

Temperature Related Failures

If the temperature is too high, greater than 60°C (150°F) (greater than 55°C (131°F) with newer type cells) the Cathode releases oxygen and the Anode has a SEI layer breakdown.
There is an increased risk of thermal runaways!
With too high of a temperature, the Electrolyte decays.

If the cell temperature is too low, less than 15-20°C (59-68°F) at a high C-rate, the Cathode is stressed from too high of a lithium-ion flow and breakage and cracks occur during discharge.
If the temperature is too low, Lithium-Plating occurs during the charge on the Anode.

Discharge Rate and Charge Rate Failures

If the discharge rate is too high, the Cathode suffers from oxidation of electrolyte (especially at high temp) and there is stress caused by the high lithium-ion flow. That stress causes breaks and cracks in the Cathode, especially at low temperatures.
If the discharge rate is too high, the Anode accumulates products of degradation from the electrolyte.

If the charge rate is too high, and in particular at low temperature, the Anode suffers from plating.

Cell Puffing Failures

"Puffed" cells are divided into two different types:

"Reversible" puffing occurs in a high-current discharge. The cell reforms after cooling back down. This is basic puffing caused by the evaporative components of the solvent in the electrolyte. It is a sign of a current overload, but cell can still be used.

"Irreversible" puffing does not reverse after cooling. Its basic cause is the decay processes of the electrolyte forming CO₂ and other gases. It is an indication of defects in the cell. The consequence is a loss of capacity and increased internal resistance. If a deep discharge occurred, immediately discard cell. There is probable damage to the cathode, which was accompanied by oxygen release.

Damaged cells smell 'sweet' or 'fruity' if electrolyte leaks. Such cells must be disposed of immediately. Only hold them with protective gloves, as the conductive salts in the electrolyte are poisonous and corrosive. Some additives are dangerous as well.

Conducting salts ("LiPo") LiPF₆:
R34: Causes burns.
R24: Toxic in contact with skin.
R22: Harmful if swallowed.

Conducting salts ("LiFePo") LiBF₄:
R20/21/22: Harmful by inhalation, and with skin contact.
R31: Contact with acids liberates toxic gas.
R34: Causes burns.
R36/37/38: Irritating to eyes, respiratory system and skin.
R23/24/25: Toxic by inhalation, in contact with skin.
R11: Highly flammable

Store cool, dry and empty (about 3.7V per cell) at or less than 20°C (68°F)
Bring the pack up to operating temperature before charging and discharging.
Never overcharge greater than 4.2V per cell, or great than 4.25V or 4.35V per cell for HV cells.
Never over-discharge to less than 3.0V per cell. If an over-discharge occurs, immediately recharge.
The cell's operating temperature should be greater than 25°C (77°F), ideally between 30°C (86°F) and 40°C (104°F)
Keep the pack at working temperature only as long as absolutely necessary
Do not operate them if overly warm, greater than 55°C (131°F) to 60°C (140°F).

Even longer life:
Do not charge to 4.2V (cycle life is doubled if charged to just 4.1V *)
Do not fully discharge, use shallow cycles (less than 70% DOD doubles lifespan *)
Use low loads and do not load quickly (especially at low temperatures)
* especially for low loads