Week 1 Understanding Different Battery Chemistry

1. Prepare a table which includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP and LTO type of lithium ion cells.Give your detailed explanation on it

Lithium-ion battery chemistry

As the name suggests, lithium ions (Li⁺) are involved in the reactions driving the battery. Both electrodes in a lithium-ion cell are made of materials which can intercalate or ‘absorb’ lithium ions Intercalation is when charged ions of an element can be ‘held’ inside the structure of a host material without significantly disturbing it. In the case of a lithium-ion battery, the lithium ions are ‘tied’ to an electron within the structure of the anode. When the battery discharges, the intercalated lithium ions are released from the anode, and then travel through the electrolyte solution to be absorbed (intercalated) in the cathode.

The cathodes used in lithium-ion batteries

LITHIUM COBALT OXIDE (LiCoO₂)

The most common lithium-ion cells have an anode of carbon (C) and a cathode of lithium cobalt oxide (LiCoO₂). In fact, the lithium cobalt oxide battery was the first lithium-ion battery to be developed from the pioneering work of R Yazami and J Goodenough, and sold by Sony in 1991. 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.

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.

• At the anode, lithium is oxidised. Lithium ions are released from the carbon, along with electrons:

  LiC6→xLi++xe−+C6LiC6→xLi++xe−+C6

  At the cathode, lithium-ions are absorbed by the lithium dioxide, and the electrode is reduced as it also receives the electrons from the circuit:

  Li1−xCoO2+xLi++xe−→LiCoO2Li1−xCoO2+xLi++xe−→LiCoO2

  The overall reaction is:

  C6+LiCoO2⟷LixC6+Li1−xCoO2C6+LiCoO2⟷LixC6+Li1−xCoO2

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.

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.S

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.

LITHIUM POLYMER

Replacing the liquid electrolyte in a lithium-ion battery with a solid electrolyte improves the battery’s safety and makes it lighter. As the polymer itself is extremely thin, it also enables greater flexibility in terms of shape and design—it need not be contained in a rigid case, and can be made to be extremely compact.

The polymer electrolyte is a non-conducting material that still allows ion exchange. In early designs the polymer was such a poor conductor that it was unable to facilitate ion exchange unless heated to around 60 degrees Celsius, so small amounts of gel are now added to avoid this issue.

2. Compare the differences between each type of Li+ion battery based on their characteristics