What Makes Up A Lithium-ion Battery?
A battery is made up of a positive electrode (cathode), negative electrode (anode), and an electrolyte to allow the flow of electrical charge between the two electrodes.
In a conventional lithium-ion battery cell, the negative electrode is usually made from carbon. The positive electrode is a metal oxide, and the electrolyte is a mixture of lithium salt and organic solvent.
To make a battery viable as an electric storage device, eight basic requirements must be met. These are as follows.
- High specific energy (long runtime): Lithium-ion is synonymous with a high specific energy
- High specific power (instantaneous power output): This is usually achieved at the expense of specific energy
- Affordable price: Materials, refining processes, manufacturing, quality control and cell matching add cost for battery manufacturing
- Long life: Longevity does not depend on battery design alone but also on how the battery is used. Adverse temperature, fast charge times and harsh discharge conditions stress the battery.
- Safety: Lithium-based batteries can be built with high specific energy, but can be reactive and unstable. When used correctly, brand-name Li-ion is very safe.
- Wide operating range: Cold temperatures slow the electrochemical reaction of all batteries, and high heat shortens battery life and compromises safety.
- Toxicity: Cadmium and mercury-based batteries have been replaced with alternative metals for environmental reasons.
- Fast charging: Fast charge times are possible for nickel and lithium, but the batteries must be built for it, be in good condition and be charged at room temperature.
Possible 9th and 10th requirements could be having low self-discharge to allow long shelf life with minimal performance degradation over time, and providing an instant start-up when needed.
Types of Lithium-ion Battery
Lithium-ion batteries are referenced by their active chemical makeup (e.g. lithium cobalt oxide has the chemical symbols LiCoO2 and can be abbreviated to LCO or Li-cobalt). A list of commonly used chemistries are described below.
Lithium Cobalt Oxide (LiCoO2 or LCO)
Common Uses: Mobile phones, laptops and digital cameras
Li-cobalt has high energy density, a relatively short life span, low thermal stability (safety risk – especially when damaged) and limited load capabilities (specific power). Newer systems include nickel, manganese and/or aluminum to improve longevity, loading capabilities and cost.
Lithium Manganese Oxide (LiMn2O4 or LMO)
Common Uses: Power tools, medical instruments, hybrid/electric vehicles (e.g. Nissan Leaf, Chevy Volt and BMW i3)
High thermal stability and enhanced safety, but life is limited. Low internal cell resistance enables fast charging and high-current discharging. Pure Li-manganese batteries are no longer common today; with most now blended with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span.
Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2 or NMC)
Common Uses: power tools, e-bikes, automotive, and energy storage systems (ESS).
One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). The secret of NMC lies in combining nickel and manganese. While toxic on their own, mixing them serves to enhance each other strengths. NMC offers lower energy density, but a longer life and inherent safety with the lowest self-heating rate.
Lithium Iron Phosphate (LiFePO4 or LFP)
Common Uses: bicycles, electric cars, solar lighting, and energy storage systems (ESS).
The key benefits are long cycle life, 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, but offers lower energy density.
Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2 or NCA)
Common Uses: specialty designs aimed at particular niche roles.
Lithium nickel cobalt aluminum oxide shares similarities with NMC by offering high specific energy, reasonably good specific power and a long life span. Less flattering are safety and cost. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.
Lithium Titanate (Li4Ti5O12)
Common Uses: electric powertrains, UPS and solar-powered street lighting.
Li-titanate is safe and has excellent low-temperature discharge characteristics; however the battery is very expensive and has lower specific energy.
For more info: Battery University