Week 1 Understanding Different Battery Chemistry

Li-ion batteries consist of largely four main components: cathode, anode, electrolyte, and separator.
Every single component of a Li-ion battery is essential as it cannot function when one of the components is missing.

The Four Components of Li-ion Battery​

“Cathode” determines the capacity and voltage of a Li-ion battery

 A Lithium-ion battery generates electricity through chemical reactions of lithium.

This is why, of course, lithium is inserted into the battery and that space for lithium is called “cathode”.

However, since lithium is unstable in the element form, the combination of lithium and oxygen, lithium oxide is used for cathode.

The material that intervenes the electrode reaction of the actual battery just like lithium oxide is called ”active material”.

In other words, in the cathode of a Li-ion battery, lithium oxide is used as an active material. 

Cathode plays an important role in determining the characteristics of the battery

as the battery’s capacity and voltage are determined by active material type used for cathode.

The higher amount of lithium, bigger the capacity; and the bigger potential difference between cathode and anode, higher the voltage.

The potential difference is small for anode depending on their type but for cathode, the potential difference is relatively high in general.

As such, the cathode plays a significant role in determining the voltage of the battery. 

▶ ”Anode” sends electrons through a wire

Just like the cathode, the anode substrate is also coated with active material.

The anode’s active material performs the role of enabling electric current to flow through the external circuit

while allowing reversible absorption/emission of lithium ions released from the cathode.

When the battery is being charged, lithium ions are stored in the anode and not the cathode.

At this point, when the conducting wire connects the cathode to the anode (discharge state),

lithium ions naturally flow back to the cathode through the electrolyte,

and the electrons (e-) separated from lithium ions move along the wire generating electricity.

For anode graphite which has a stable structure is used, and the anode substrate is coated with active material,

conductive additive and a binder.

Thanks to graphite’s optimal qualities such as structural stability, low electrochemical reactivity,

conditions for storing much lithium ions and price, the material is considered suitable to be used for anode.

▶ “Electrolyte” allows the movement of ions only

 When explaining about cathode and anode, it was mentioned that lithium ions move through the electrolyte

and electrons move through the wire.

This is the key in enabling the use of electricity in a battery.

If ions flow through the electrolyte, not only can’t we use electricity but safety will be jeopardized.

Electrolyte is the component which plays this important role.

It serves as the medium that enables the movement of only lithium ions between the cathode and anode.

For the electrolyte, materials with high ionic conductivity are mainly used so that lithium ions move back and forth easily. 

The electrolyte is composed of salts, solvents and additives.

The salts are the passage for lithium ions to move, the solvents are organic liquids used to dissolve the salts,

and the additives are added in small amounts for specific purposes. 

Electrolyte created in this way only allows ions to move to the electrodes and doesn’t let electrons to pass.

In addition, the movement speed of lithium ions depends on the electrolyte type.

Thus, only the electrolytes that meet stringent conditions can be used.

▶ ”Separator”, the absolute barrier between cathode and anode

 While the cathode and anode determine the basic performance of a battery, electrolyte and separator determine the safety of a battery.  

The separator functions as a physical barrier keeping cathode and anode apart.

It prevents the direct flow of electrons and carefully lets only the ions pass through the internal microscopic hole

Therefore, it must satisfy all the physical and electrochemical conditions.

Commercialized separators we have today are synthetic resin such as polyethylene (PE) and polypropylene (PP).

 So far, we have looked at the four main components which determine the performance of Li-ion batteries.

Currently, Samsung SDI is strengthening R&D of new materials for the enhancement of battery performance

while ceaselessly continuing its efforts to improve the performance of existing materials and core technologies.

The cobalt and oxygen bond together to form layers of octahedral cobalt oxide structures, separated by sheets of lithium. It’s important that this structure allows the cobalt ions to change their valence states between Co⁺³ and Co⁺⁴ (lose and gain a negatively-charged electron) when charging and discharging.

LITHIUM COBALT OXIDE (LiCoO₂)

Of all the various lithium-ion batteries, these guys have the greatest energy density, which is why they’re currently the batteries found in our phones, digital cameras and laptops. Their drawback is their thermal instability. Their anodes can overheat and, at high temperatures, the cobalt oxide cathode can decompose, producing oxygen. If you combine oxygen and heat, you’ve got a pretty good chance of starting a fire and, as the chemicals sometimes used in the electrolyte solution, such as diethyl carbonate, are flammable, there can be some safety issues with this battery. 

Lithium-ion batteries have in-built protections to prevent overheating, and to prevent the complete discharge of the battery which can also be damaging. Additionally, these protection circuits can sometimes be used to prevent over-charging of lithium-ion batteries, which can have serious consequences. Lithium-ion batteries come in a wide variety of shapes and sizes, and some contain in-built protection devices, such as venting caps, to improve safety. 

LITHIUM IRON PHOSPHATE (LiFePO₄)

This cell has a high discharge rate and, because phosphate (PO₄) can cope with high temperatures, the battery has good thermal stability, improving its safety. This makes it a good choice for things like electric vehicles and power tools, and for storing energy at power stations. It also has a long cycle life, meaning it can be discharged and charged many times. However, it has a lower energy density than a lithium cobalt oxide cell, and a higher self-discharge rate.

A lithium iron phosphate battery cell is similar to the lithium cobalt oxide cell. The anode is still graphite and the electrolyte is also much the same. The difference is that the lithium cobalt dioxide cathode has been replaced with the more stable lithium iron phosphate. In fact, no lithium or iron ions remain in the iron phosphate (FePO4) cathode of a fully charged cell. The lithium ions can intercalate into or out of the cathode material through well-defined tunnels in its structure without significantly altering the iron phosphate framework. 

LITHIUM MANGANESE OXIDE (LiMn₂O₄)

This type of lithium battery uses a cathode made from lithium-manganese spinel (Li⁺Mn³⁺Mn⁴⁺O₄). Spinel is a type of mineral with a distinctive AB₂O₄ structure. The spinel structure has very good thermal stability, improving the battery’s safety. It also promotes ion flow within the electrolyte and lessens the internal resistance that contributes to the loss of a battery’s power over time. 

While this type of lithium battery offers high discharge and recharge rates (also due to the spinel structure of the cathode) it has a lower capacity and shorter lifetime. 

LITHIUM NICKEL MANGANESE COBALT OXIDE (LiNiMnCoO₂ or NMC)

Adding nickel and cobalt back into the mix changes things slightly again. Nickel provides a high specific energy and, when added to the stable structure of the manganese spinel, also results in a battery with the benefits of the manganese spinel structure (low internal resistance, high charging rate, good stability and safety).  

These batteries are generally made with a cathode with one-third nickel, one-third manganese and one-third cobalt, but the ratio can vary according to manufacturers’ secret formulas. These batteries are used in power tools, electric vehicles and medical devices.

Lithium manganese batteries are often coupled with a lithium nickel manganese cobalt oxide battery, producing a combination that is used in many electric vehicles. High bursts of energy (for rapid acceleration) are provided by the lithium-manganese component, and a long driving range is provided by the lithium nickel manganese cobalt oxide component.

The cathode of this type of cell is made of negatively charged phosphate anions, bonded with positively charged iron cations in a structure that is capable of storing lithium ions within the iron phosphate molecules. The bonding arrangement in this structure means that the oxygen atoms are tightly bonded into the structure, which gives the cathode its chemical stability.

Lithium nickel cobalt aluminum oxide:

Lithium nickel cobalt aluminum oxide batteries are not conventional in the consumer industry but have promise for EV manufacturers (and other specialized applications), as they provide high-specific energy options, reasonably good specific power, and a decent lifespan.

These types are not as safe as the others listed here and as such, require special safety monitoring measures to be employed for use in EVs. They are also more costly to manufacture, limiting their viability for use in other applications.

2. 

There are different types of lithium-ion batteries and the main difference between them lies in their cathode materials. Different kinds of lithium-ion batteries offer different features, with trade-offs between specific power, specific energy, safety, lifespan, cost, and performance.

The six lithium-ion battery types that we will be comparing are Lithium Cobalt Oxide, Lithium Manganese Oxide, Lithium Nickel Manganese Cobalt Oxide, Lithium Iron Phosphate, Lithium Nickel Cobalt Aluminum Oxide, and Lithium Titanate. Firstly, an understanding of the key terms below will allow for a simpler and easier comparison.

Performance: This measures how well the battery works over a wide range of temperatures. Most batteries are sensitive to heat and cold and require climate control. Heat reduces life, and cold lowers performance temporarily.

Lifespan: This reflects cycle life and longevity and is related to factors such as temperature, depth of discharge, and load. Hot climates accelerate capacity loss. Cobalt blended lithium-ion batteries also usually have a graphite anode that limits the cycle life.

Safety: This relates to factors such as the thermal stability of the materials used in the batteries. The materials should have the ability to sustain high temperatures before becoming unstable. Instability can lead to thermal runaway in which flaming gases are vented. Fully charging the battery and keeping it beyond the designated age reduces safety.

Cost: Demand for electric vehicles has generally been lower than anticipated and this is mainly due to the cost of lithium-ion batteries. Hence cost is a huge factor when selecting the type of lithium-ion battery.