Week 1 Understanding Different Battery Chemistry

1. AIM

Prepare a table that includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP, and LTO type of lithium-ion cells.

2. OBJECTIVE

To prepare a table that includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP, and LTO type of lithium-ion cells.

3. THEORY

A battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices such as flashlights, mobile phones, and electric cars. When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode. The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal. When a battery is connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically the term "battery" specifically referred to a device composed of multiple cells, however, the usage has evolved to include devices composed of a single cell.

Working Principle of Battery

A battery works on the oxidation and reduction reaction of an electrolyte with metals. When two dissimilar metallic substances, called electrodes, are placed in a diluted electrolyte, oxidation and reduction reactions take place in the electrodes respectively depending upon the electron affinity of the metal of the electrodes. As a result of the oxidation reaction, one electrode gets negatively charged called cathode and due to the reduction reaction, another electrode gets positively charged called anode.

Lithium-Ion Batteries

A lithium-ion (Li-ion) battery is an advanced battery technology that uses lithium ions as a key component of its electrochemistry. During a discharge cycle, lithium atoms in the anode are ionized and separated from their electrons. The lithium ions move from the anode and pass through the electrolyte until they reach the cathode, where they recombine with their electrons and electrically neutralize. The lithium ions are small enough to be able to move through a micro-permeable separator between the anode and cathode. In part because of lithium’s small size (third only to hydrogen and helium), Li-ion batteries are capable of having a very high voltage and charge storage per unit mass and unit volume.

Li-ion batteries can use a number of different materials as electrodes. The most common combination is that of lithium cobalt oxide (cathode) and graphite (anode), which is most commonly found in portable electronic devices such as cellphones and laptops. Other cathode materials include lithium manganese oxide (used in hybrid electric and electric automobiles) and lithium iron phosphate. Li-ion batteries typically use ether (a class of organic compounds) as an electrolyte.

Types of Lithium-Ion batteries

1. Lithium Cobalt Oxide(LiCoO2) — LCO
2. Lithium Manganese Oxide (LiMn2O4) — LMO
3. Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO₂) — NMC
4. Lithium Iron Phosphate(LiFePO4) — LFP
5. Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA
6. Lithium Titanate (Li2TiO3) — LTO

Lithium Cobalt Oxide(LiCoO2) — LCO

Its high specific energy makes Li-cobalt the popular choice for mobile phones, laptops, and digital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon anode. The cathode has a layered structure and during discharge, lithium ions move from the anode to the cathode. The flow reverses on a charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability, and limited load capabilities (specific power). Figure 1 illustrates the structure.

Lithium Manganese Oxide (LiMn2O4) — LMO

Li-ion with manganese spinel was first published in the Materials Research Bulletin in 1983. In 1996, Moli Energy commercialized a Li-ion cell with lithium manganese oxide as a cathode material. The architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improved current handling. A further advantage of spinel is high thermal stability and enhanced safety, but the cycle and calendar life is limited.

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO₂) — NMC

One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored to serve as Energy Cells or Power Cells. For example, NMC in a 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4A to 5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mAh but delivers a continuous discharge current of 20A. A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life. Silicon added to graphite has the drawback that the anode grows and shrinks with charge and discharge, making the cell mechanically unstable.

Lithium Iron Phosphate(LiFePO4) — LFP

In 1996, the University of Texas (and other contributors) discovered phosphate as cathode material for rechargeable lithium batteries. Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety, and tolerance if abused.

Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA

Lithium nickel cobalt aluminum oxide battery, or NCA, has been around since 1999 for special applications. It shares similarities with NMC by offering high specific energy, reasonably good specific power, and a long life span. Less flattering are safety and cost. Figure 11 summarizes the six key characteristics. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.

Lithium Titanate (Li2TiO3) — LTO

Batteries with lithium titanate anodes have been known since the 1980s. Li-titanate replaces the graphite in the anode of a typical lithium-ion battery and the material forms into a spinel structure. The cathode can be lithium manganese oxide or NMC. Li-titanate has a nominal cell voltage of 2.40V, can be fast charged, and delivers a high discharge current of 10C, or 10 times the rated capacity. The cycle count is said to be higher than that of a regular Li-ion. Li-titanate is safe, has excellent low-temperature discharge characteristics, and obtains a capacity of 80 percent at –30°C (–22°F).

Tabular Summary of the types of Li-ion batteries

Chemical reactions in the different batteries

1. Lithium Cobalt Oxide(LiCoO2) — LCO

At Anode

`LiC_6-> xLi^++xe^(-)+C_6`

At Cathode

`Li_(1-x)CoO_2+xLi^++xe^-)->LiCoO_2`

Overall Reaction

`C_6+LiCoO_2harrLi_xC_6+Li_(1-x)CoO_2`

2. Lithium Manganese Oxide (LiMn2O4) — LMO

At Anode

`Li->Li^++e^-`

At Cathode

`Mn_2O_4+Li^++e^-)->LiMn_2O_4`

3. Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO₂) — NMC

At Anode

`Li_xC_n->nC+xLi^++xe^-`

At Cathode

`Li_(1-x)MO_2+xLi^++xe^-)->LiMO_2`

Redox Reaction

`Li_(1-x)MO_2+Li_xC_n->LiMO_2+nC`

4. Lithium Iron Phosphate(LiFePO4) — LFP

At Anode

`LiC_6-> Li^++e^(-)+C_6`

At Cathode

`LiFe(III)PO_4+xLi^++xe^-)->LiFe(II)PO_4`

`FePO_4+Li^++e^-)->LiFePO_4`

Overall Reaction

`LiFePO_4+6C->LiC_6+FePO_4`

5. Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA

6. Lithium Titanate (Li2TiO3) — LTO

when charged/discharged in the potential range of 1.00–3.00 V

`Li_4Ti_5O_12 + 3Li^++ 3e^-)harr Li_7Ti_5O_12`

Increased capacity of lithium–titanium oxide when cycled to 0.01 V is related to a full reduction of titanium ions from +4 to +3 oxidation state which involves additional two Li+ ions

`Li_7Ti_5O_12 + 2Li^+ + 2e^-)harrLi_9Ti_5O_12`

4. LEARNING OUTCOME

From the above, we have learned all about various types of lithium-ion batteries and the reactions happening in them.