Week 1 Understanding Different Battery Chemistry

Fig1: Diagrammatic view of a lithium-ion cell

Fig2:Internal construction of a typical cylindrical cell

Fig3:Internal construction of a typical pouch cell

Fig4:CAD Of dissembeled battery module, assembled module and whole battery package

There are a range of applications for batteries in passenger cars . The ones that will be considered here were selected either because they already use lithium-ion batteries or because they could potentially do so in the future. Note that there are a number of standard automotive requirements that all lithium-ion batteries used in cars need to meet: these include life (8–15 years are typical requirements), temperature range (–40°C to at least +60°C, ideally 80°C) and vibration resistance (at least 4.5 root-mean-square-acceleration (grms)) . Each application will now be briefly described.

Cathode:

Cathode materials are generally constructed from LiCoO₂ or LiMn₂O₄. The cobalt-based material develops a pseudo tetrahedral structure that allows for two-dimensional lithium-ion diffusion. The cobalt-based cathodes are ideal due to their high theoretical specific heat capacity, high volumetric capacity, low self-discharge, high discharge voltage, and good cycling performance. Limitations include the high cost of the material, and low thermal stability.The manganese-based materials adopt a cubic crystal lattice system, which allows for three-dimensional lithium-ion diffusion. Manganese cathodes are attractive because manganese is cheaper and because it could theoretically be used to make a more efficient, longer-lasting battery if its limitations could be overcome. Limitations include the tendency for manganese to dissolve into the electrolyte during cycling leading to poor cycling stability for the cathode.Cobalt-based cathodes are the most common, however other materials are being researched with the goal of lowering costs and improving cell life.

As of 2017, LiFePO₄ is a candidate for large-scale production of lithium-ion batteries such as electric vehicle applications due to its low cost, excellent safety, and high cycle durability. For example, Sony Fortelion batteries have retained 74% of their capacity after 8000 cycles with 100% discharge. A carbon conductive agent is required to overcome its low electrical conductivity.

Positive electrode

Technology	Company	Target application	Benefit
Lithium Nickel Manganese cobalt oxide NMC, LiNixMnyCozO2	Imara Corporation, Nissan Motor, Microvast In LG Chem,Northvolt	Electric vehicles,Power tools,Grid energy stoage.	good specific energy and specific power density
Lithium Nickel Cobalt Aluminium Oxide NCA, LiNiCoAlO2	Panasonic,saft Groupe S.A.Samsung	Electric Vehicles	High specific energy, good life span
Lithium Mangnese Oxide LMO, LiMn2O4	LG chem,NEC,Samsung,Hitachi,Nissan/AESC,EnerDel	Hybride electrcic vehicle,Cell phone,laptop
Lithium Iron Phosphate LFP, LiFePO4	Phostech Lithium Inc., Valence Technology,A123system/MIT	power tools, aviation products, automotive hybrid systems, PHEV conversions	moderate density (2 A·h outputs 70 amperes) High safety compared to Cobalt / Manganese systems. Operating temperature >60 °C (140 °F)
Lithium Cobalt Oxide LCO, LiCoO2	Sonyfirst commercial production	broad use, laptop	High specific energy

Anode:

Negative electrode materials are traditionally constructed from graphite and other carbon materials, although newer silicon-based materials are being increasingly used (see Nanowire Battery). These materials are used because they are abundant and are electrically conducting and can intercalate lithium ions to store electrical charge with modest volume expansion (~10%).Graphite is the dominant material because of its low voltage and excellent performance. Various materials have been introduced, but their higher voltage reduces low energy density. Low voltage is the key requirement; otherwise, the excess capacity is useless in terms of energy density.

Negative electrode

Technology	Density	Durability	Company	Target application
Graphite	Weight: 260 wh/kg		Tesla	The dominant negative electrode material used in lithium ion batteries, limited to a capacity of 372 mAh/g	.
Lithium Titanate LTO, Li4Ti5O12			Toshiba, Altairnano	Automotive,electrical grid (PJM Interconnection Regional Transmission Organization control area, United States Deparment Of Defense), bus (Proterra)
Hard Carbon			Energ2	Home electronics
Tin/Cobalt Alloy			Sony	Consumer electronics (Sony Nexelion battery)
Silicon/Carbon	Volumetric: 730 W·h/l Weight: 450 W-h/kg		Amprius	Smartphones, providing 5000 mA·h capacity

As graphite is limited to a maximum capacity of 372 mAh/g much research has been dedicated to the development of materials that exhibit higher theoretical capacities, and overcoming the technical challenges that presently encumber their implementation. The extensive 2007 Review Article by Kasavajjula et al. summarizes early research on silicon-based anodes for lithium-ion secondary cells. In particular, Hong Li et al. showed in 2000 that the electrochemical insertion of lithium ions in silicon nanoparticles and silicon nanowires leads to the formation of an amorphous Li-Si alloy. The same year, Bo Gao and his doctoral advisor, Professor Otto Zhou described the cycling of electrochemical cells with anodes comprising silicon nanowires, with a reversible capacity ranging from at least approximately 900 to 1500 mAh/g.

To improve stability of the lithium anode, several approaches of installing a protective layer have been suggested.Silicon is beginning to be looked at as an anode material because it can accommodate significantly more lithium ions, storing up to 10 times the electric charge, however this alloying between lithium and silicon results in significant volume expansion (ca. 400%), which causes catastrophic failure for the cell.Silicon has been used as an anode material but the insertion and extraction of {\displaystyle {\ce {\scriptstyle Li+}}} can create cracks in the material. These cracks expose the Si surface to an electrolyte, causing decomposition and the formation of a solid electrolyte interphase (SEI) on the new Si surface (crumpled graphene encapsulated Si nanoparticles). This SEI will continue to grow thicker, deplete the available {\displaystyle {\ce {\scriptstyle Li+}}}, and degrade the capacity and cycling stability of the anode.

Electrochemistry:

The reactants in the electrochemical reactions in a lithium-ion cell are materials of anode and cathode, both of which are compounds containing lithium atoms. During discharge, an oxidation half-rection at the anode produces positively charged lithium ions and negatively charged electrons. The oxidation half-reaction may also produce uncharged material that remains at the anode. Lithium ions move through the electrolyte, electrons move through the external circuit, and then they recombine at the cathode (together with the cathode material) in a reduction half-reaction. The electrolyte and external circuit provide conductive media for lithium ions and electrons, respectively, but do not partake in the electrochemical reaction. During discharge, electrons flow from the negative electrode (anode) towards the positive electrode (cathode) through the external circuit. The reactions during discharge lower the chemical potential of the cell, so discharging transfers energy from the cell to wherever the electric current dissipates its energy, mostly in the external circuit. During charging these reactions and transports go in the opposite direction: electrons move from the positive electrode to the negative electrode through the external circuit. To charge the cell the external circuit has to provide electric energy. This energy is then stored as chemical energy in the cell (with some loss, e. g. due to coulombic efficiency lower than 1).

Both electrodes allow lithium ions to move in and out of their structures with a process called insertion or extrction respectively.

As the lithium ions "rock" back and forth between the two electrodes, these batteries are also known as "rocking-chair batteries" or "swing batteries" (a term given by some European industries).

The following equations exemplify the chemistry.

The positive electrode (cathode) half-reaction in the lithium-doped cobalt oxide substrate is

{\displaystyle {\ce {CoO2 + Li+ + e- <=> LiCoO2}}}

The negative electrode (anode) half-reaction for the graphite is

{\displaystyle {\ce {LiC6 <=> C6 + Li+ + e^-}}}

The full reaction (left to right: discharging, right to left: charging) being

{\displaystyle {\ce {LiC6 + CoO2 <=> C6 + LiCoO2}}}

The overall reaction has its limits. Overdischarging supersaturates lithium cobalt oxide, leading to the production of lithium oxide, possibly by the following irreversible reaction:

{\displaystyle {\ce {Li+ + e^- + LiCoO2 -> Li2O + CoO}}}

Overcharging up to 5.2 volts leads to the synthesis of cobalt (IV) oxide, as evidenced by x-ray differaction.

{\displaystyle {\ce {LiCoO2 -> Li+ + CoO2 + e^-}}}

In a lithium-ion cell, the lithium ions are transported to and from the positive or negative electrodes by oxidizing the transition metal, cobalt (Co), in Li_1-xCoO₂ from Co³⁺ to Co⁴⁺ during charge, and reducing from Co⁴⁺ to Co³⁺ during discharge. The cobalt electrode reaction is only reversible for x < 0.5 (x in mole units), limiting the depth of discharge allowable. This chemistry was used in the Li-ion cells developed by Sony in 1990.

The cell's energy is equal to the voltage times the charge. Each gram of lithium represents Faraday's Constant/6.941, or 13,901 coulombs. At 3 V, this gives 41.7 kJ per gram of lithium, or 11.6 kWh per kilogram of lithium. This is a bit more than the heat of combustion of gasoline but does not consider the other materials that go into a lithium battery and that make lithium batteries many times heavier per unit of energy.

The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions will electrolyze.

1)Lithium cobalt oxide barrey:

Lithium cobalt oxide (LiCoO₂) is a common cathode material in lithium ion (Li-ion) batteries whose cathode is composed of lithium cobalt oxide (LiCoO₂). They are widely used for powering mobile phones, laptops, video cameras, and other modern day electronic gadgets.Lithium ion batteries commonly use graphite and cobalt oxide as additional electrode materials. Lithium ion batteries work by using the transfer of lithium ions and electrons from the anode to the cathode. At the anode, neutral lithium is oxidized and converted to Li+.

2)Lithium-ion mangnese oxide battery:

A lithium ion manganese oxide battery (LMO) is a lithium-ion cell that uses manganese dioxide, Mno2, as the cathode material. They function through the same intercalation/de-intercalation mechanism as other commercialized secondary battery technologies, such as LoCoO2. Cathodes based on manganese-oxide components are earth-abundant, inexpensive, non-toxic, and provide better thermal stability.

3)Lithium Nickel Cobalt Aluminium Oxide battery:

The lithium nickel cobalt aluminium oxides (NCAs) are a group of mixed metal oxides. Some of them are important due to their application in lithium ion batteries. NCAs are used as active material on the positive pole (which is the cathode when the battery is discharged).

4)Lithium Nickel Mangnese Cobalt oxide battery:

Nickel manganese cobalt batteries. This is one of the most famous lithium ion systems which have a cathode combination of nickel-manganese-cobalt. This system can be used to operate as power cells or energy cells. The components of NMC are combined and made with nickel and manganese.

5)Lithium Iron Phosphate Batteries:

Lithium iron phosphate batteries (LiFePO4 or LFP) offer lots of benefits compared to lead-acid batteries and other lithium batteries. Longer life span, no maintenance, extremely safe, lightweight, improved discharge and charge efficiency, just to name a few. LiFePO4 batteries are not the cheapest in the market, but due to a long life span and zero maintenance, it’s the best investment you can make over time.

6)Lithium-Titanate-oxide battery:

The lithium-titanate or lithium-titanium-oxide (LTO) battery is a type of rechargeable battery which has the advantage of being faster to charge than other lithium-ion batteries, but the disadvantage of having a much lower energy density.