Week 1 Understanding Different Battery Chemistry

Fundamental chemical process: Lithium-ion cell:

• While discharging, negative electrode (Anode) gives up electrons and gets oxidized.
• While charging, negative electrode accepts electrons & gets reduced.
• It is also known as reduction – oxidation reactions / redox reaction.
• Li ion has 1 unbalanced electron and it is very reactive or an aggressive donor of electron outside its periphery.
• Li+ ion gives up the charged ion.
• The Li+ ions keep shuttling between electrodes.
• Li+ transfer from anode (negative terminal) to cathode (positive terminal) while discharging and from Cathode (positive terminal) to Anode (negative terminal) when charging
• A discharged Li Ion Battery will have Li ions placed in the negative electrode.
• A charged Li ion Battery will have Li ions placed in the positive electrode.
• Positively charged ions are called cations and negatively charged ions are called anions.
• Cations move through the electrolyte from one electrode to another.
• Separator does not allow electrons to pass through it, hence the electrons move through the external electric circuit.
• 

Lithium-ion cathode (positive) Materials:

• Li ion cells are classified based on material used at the Cathode
• Layered transition-metal oxides: Highest capacity but cost and safety are a concern. (NCA, NMC, LCO)
  LCO is not preferred for EV applications because of safety concerns, but for low voltage requirements such as consumer products such as remotes, etc.
• Spinels: High power density, but poor electronic conductivity and structural stability (LMO, LTO)
• Olivines: Better safety and longer life but low capacity and voltage (LiFePO4)
• LiPo – Li polymer

Lithium-Ion anode material:

• Carbon Based anode: Graphite or hard Carbon
• Low cost, stable and high specific capacity.
• Issue: Lithium plating – When the potential of the anode becomes excessively low, Li-ions can plate out as metallic lithium on the surface of the anode.
• Dendrite formation may result into short circuiting and may result into thermal run away, capacity loss

Lithium-Ion electrolyte material:

• A mixture of organic solvents which contain lithium salt. Such as:

1. Ethylene carbonate
2. Dimethyl carbonate
3. Propylene carbonate

• For carbon anodes operating at a potential close to the plating of lithium, this causes the reduction of the electrolyte at the anode, building a protective coating known as SEI layer (Solid electrolyte interface)
• Typically formed during the first few charges cycles
• Below 0 C, the ionic transport properties suffer, which can drastically lower cell performance and efficiency. Difficult to use li ion cells at low temperatures.

Trade offs among 5 main lithium battery technologies:

1. Lithium-Nickel manganese Cobalt (NMC): Most commonly used and covers the most chart area among all different chemistries. Used in power tools and powertrains of EV.
   • High specific energy.
   • Moderate on Cost Effectiveness, Life Span, Performance Safety and Specific Power.
   • They can either have high specific energy density or high specific power. They cannot have both properties.
   • May come down in price as some manufacturers are planning on having higher% of nickel and save cost by reducing % of Cobalt.
   • Preferable for EVs because of their low self heating rate.
2. Lithium Nickel Cobalt aluminium (NCA): Preferrable on all aspects except that it is high on cost and has safety related concerns.
   • High Specific energy, Specific power, Life span
   • Moderate on performance
   • Poor in terms of safety and Cost effectiveness
   • Most commonly used in consumer industries, But are promising for EV. Currently not in use for EV because of safety concerns.
3. Lithium Manganese Spinel (LMO):
   • Poor in terms of lifespan and performance
   • Moderate in terms of Safety, Specific power, Specific energy and Cost.
   • They are notable for high temperature stability and are also safer than other li ion battery types.
   • Often used in medical devices.
4. Lithium Titanate (LTO): Most expensive among all other chemistries. But best for performance, Lifespan and safety.
   • Poor in terms of specific energy and specific power.
   • Excellent in terms of Safety, Performance and Life span
   • But most expensive in the category
   • Allows ever increasing applications, remarkably fast charging time.
   • Manufacturers of EV and E bikes use Lithium Titanate, and there is a potential of its use in similar application on a large scale.
   • However, they have lower inherent voltage, or low energy density than others.
5. Lithium Iron phosphate (LFP): Another widely used form of chemistry. Also referred as LiFePo4
   • Excellent in terms of lifespan and safety
   • Moderate on Performance, specific power and Cost effectiveness
   • Poor specific energy
   • They have low resistance properties which enhance their safety and thermal stability.
   • Durability and long-life cycles are another advantage, fully charged batteries can be stored with little change in total lifespan of battery’s charge
   • Also cost effective when battery life is taken into account.
   • Used in applications which need long charging time and safety, such as e bikes.
6. LCO Lithium cobalt oxide:
   • High specific energy, making it suitable for mobile phones, Laptops, etc
   • Low lifespan and low thermal stability

Li-Ion Cell Type	Cathode	Anode	Electrolyte	Separator	Overall reaction at Cathode and Anode	Applications
LCO	Lithium Cobalt Oxide (LiCoO2)	Graphite Carbon	Ethylene Carbonate + Li salt	Polyolefin	Li(1-x) CoO2(s) + x Li+ + x e- → LiCoO2 (s)	Mobile phones, Laptop, Cameras
LMO	Lithium Manganese Oxide (LiMn2O4)	Graphite Carbon	Methyl Carbonate + Li salt	Polyolefin	Mn2+ + 2LiC6 → Mn + 2Li+ + graphite	Power Tools, Medical Equipment
NCA	Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2)	Graphite Carbon	Propylene Carbonate + Li salt	Polyolefin	Li(1-x) NiO2 → (2-x) Li (1 -x)/(2-x) O + x/2O2	Tesla, Industrial electric powertrain
NMC (NCM)	Lithium Nickel Cobalt Manganese Oxide (LiNiCoMnO2)	Graphite Carbon	Methyl Carbonate + Li Salt	Polyolefin	Li(x)MO2 (s) → Li+(org) + Li(x-1) MO2(s) + e-	E bikes, medical device, Ev
LFP	Lithium Iron Phosphate (LiFePO4/C)	Graphite Carbon	Propylene Carbonate + Li salt	Polyolefin	LiFeIIPO4 ↔ FEIIIPO4 Li+ +e-	High load currents and endurance UPS
LTO	Lithium Titanium Oxide	Graphite Carbon	Propylene Carbonate + Li salt	Polyolefin	Li4Ti5O12 +3Li+ + 3e → 4Li7Ti5O12	Electric powertrain (Mitsubishi i-MiEV, Honda fit EV