Challenge

Week 1 Understanding Different Battery Chemistry

MManobala S30 Nov 2022

Battery Type	Material		Electrolyte		Reactions (Discharge)
Battery Type	Cathode	Anode	Salt	Solvent	Anode	Cathode
LCO	LiCoO₂	Graphite	LiPF₆	Ethylene Carbonate	C₆Li --> 6C + Li⁺+ e^-	Li_1-xCoO₂+ xLi⁺+ xe^- --> LiCoO₂
LMO	LiMn₂O₄	Graphite	LiPF₆	Ethylene Carbonate	C₆Li --> 6C + Li⁺+ e^-	Li_1-xMn₂O₄+ xLi⁺+ xe^- --> LiMn₂O₄
NCA	LiNiCoAlO₂	Graphite	LiPF₆	Ethylene Carbonate	C₆Li --> 6C + Li⁺+ e^-	Li_1-xNiCoAlO₂+ xLi⁺+ xe^- --> LiNiCoAlO₂
NMC	LiNiMnCoO₂	Graphite	LiPF₆	Ethylene Carbonate	C₆Li --> 6C + Li⁺+ e^-	Li_1-xNiMnCoO₂+ xLi⁺+ xe^- --> LiNiMnCoO₂
LFP	LiFePO₄	Graphite	LiPF₆	Ethylene Carbonate	C₆Li --> 6C + Li⁺+ e^-	Li_1-xFePO₄+ xLi⁺+ xe^- --> LiFePO₄
LTO	LiMn₂O₄	Titanate	LiPF₆	Ethylene Carbonate	Li₇Ti₅O₂₂ à Li₄Ti₅O₂₂ + 3Li⁺+ 3e^-	Li_1-xMn₂O₄+ xLi⁺+ xe^- à LiMn₂O₄

LCO - Lithium Cobalt Oxide (LiCoO₂)

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 charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability, and limited load capabilities (specific power). Like other cobalt-blended Li-ion, Li-cobalt has a graphite anode that limits the cycle life by a changing solid electrolyte interface (SEI), thickening on the anode, and lithium plating while fast charging and charging at low temperatures.

Li-cobalt should not be charged and discharged at a current higher than its C-rating. This means that a 18650 cell with 2,400mAh can only be charged and discharged at 2,400mA. Forcing a fast charge or applying a load higher than 2,400mA causes overheating and undue stress. The mandatory battery protection circuit limits the charge and discharge rate to a safe level of about 1C for the Energy Cell. The picture below shows the performance of the battery,

LMO - Lithium Manganese Oxide (LiMn₂O₄)

Li-ion cell with lithium manganese oxide as 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.

Low internal cell resistance enables fast charging and high-current discharging. In a 18650 package, Li-manganese can be discharged at currents of 20–30A with moderate heat buildup. It is also possible to apply one-second load pulses of up to 50A. A continuous high load at this current would cause heat buildup and the cell temperature cannot exceed 80°C (176°F). Li-manganese is used for power tools, medical instruments, as well as hybrid and electric vehicles. The picture below shows the performance of the battery,

NMC - Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO₂)

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 conditions 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.

The secret of NMC lies in combining nickel and manganese. Nickel is known for its high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers low specific energy. Combining the metals enhances each other strengths.

NMC is the battery of choice for power tools, e-bikes, and other electric powertrains. The cathode combination is typically one-third nickel, one-third manganese, and one-third cobalt, also known as 1-1-1. Cobalt is expensive and in limited supply. Battery manufacturers are reducing the cobalt content with some compromises in performance. A successful combination is NCM532 with 5 parts nickel, 3 parts cobalt, and 2 parts manganese. Other combinations are NMC622 and NMC811. Cobalt stabilizes nickel, a high-energy active material. The picture below shows the performance of the battery,

NCA - Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO₂)

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.

The picture below shows the performance of the battery,

LFP - Lithium Iron Phosphate (LiFePO₄)

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.

Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. As a trade-off, its lower nominal voltage of 3.2V/cell reduces the specific energy below that of cobalt-blended lithium-ion. With most batteries, cold temperature reduces performance and elevated storage temperature shortens the service life, and Li-phosphate is no exception. Li-phosphate has a higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. This can be mitigated by buying high quality cells and/or using sophisticated control electronics, both of which increase the cost of the pack. Cleanliness in manufacturing is of importance for longevity. There is no tolerance for moisture, lest the battery will only deliver 50 cycles. The picture below shows the performance of the battery,

LTO - Lithium Titanate (Li₂TiO₃)

Li-titanate replaces the graphite in the anode of a typical lithium-ion battery and the material forms 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).

LTO has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation, and no lithium plating when fast charging and charging at low temperatures. Thermal stability under high temperatures is also better than other Li-ion systems; however, the battery is expensive. The picture below shows the performance of the battery,

Differences between each type of Li-ion battery based on their characteristics:

Characteristics	LCO	LMO	NMC	NCA	LFP	LTO
Specific Energy (Capacity) [Wh/kg]	150-200	100-150	150-220	200-260	90-120	50-80
C-rate (Charge) [C]	0.7-1	0.7-1	0.7-1	0.7	1	1
C-rate (Discharge) [C]	1	1	1	1	1	10
Cycle life	500-1000	300-700	1000-2000	500	2000	3000-7000
Thermal Runaway [^oC]	150	250	210	150	270	Safest
Comments	Very high specific energy, limited specific power	High power but less capacity; Safer than LCO	Provides high capacity and high power	Shares similarities with LCO; Serves as Energy Cell	Low capacity. One of the safest Li-ions. Elevated self-discharge.	Long life, fast charge, and wide temperature range but low specific energy and is expensive.

References:

Week 1 Understanding Different Battery Chemistry

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