Lithium-ion batteries are the most popular products used for solar electricity storage today. Within the umbrella category of lithium-ion batteries, there are several specific chemistries that battery manufacturers employ in their products. These chemistries each have their own advantages and disadvantages, as well as ideal use cases.
An industry insider’s snapshot of Li-ion battery cells, covering the most popular sizes, formats, and chemistries. Given the diversity of Li-ion cells available, the focus is on cylindrical and prismatic cells in metal cases.
What you’ll learn:
● The latest trends in lithium-ioncell sizes, formats, and chemistries.
● What are the performance characteristics of popularlithium-ion cells?
● Who are the major cell suppliers for each lithium-ion cell chemistry?
Lithium-ion cells come in three basic form factors: cylindrical, prismatic (or brick-shaped), and the flat rectangular shape of lithium-polymer cells. The standard formats for metal-encased cylindrical cells are 18650 (18 mm in diameter × 65 mm tall), 21700 (21 × 70 mm), or 26650 (26 × 65 mm). Within cylindrical and prismatic cells, layers of battery material are rolled inside like a jelly roll. Lithium-ion cylindrical and prismatic cells are packaged in metal cans.
Prismatic, or brick-shaped, cells are often cost-effective and available in myriad sizes. One of the major features of a prismatic cell is the pressure vent with terminals on top of the metal can. The positive and negative terminals on the prismatic cell are tabs protruding from the cell. In multi-cell battery packs with space constraints, prismatics are recommended as their rectangular shape results in minimal air gaps between the cells.
Some of the most common types include:
● Lithium iron phosphate (LFP)
● Lithium nickel manganese cobalt oxide (NMC)
● Lithium manganese oxide (LMO)
● Lithium nickel cobalt aluminum oxide (NCA)
However, material handling equipment is typically powered by either lithium iron phosphate or lithium nickel manganese cobalt oxide chemistries.
Below we’ll explore these chemistries and how they play a role in making lithium-ion batteries one of the most popular choices of power for material handling equipment.
The LFP chemistry also offers good electrochemical performance with low impedance, as it uses a phosphate material for the cathode. Key advantages are high current delivery and exceptional cycle life, good thermal stability, and superior safety against abusive conditions. These types of cells have an intrinsically safer cathode material than NMC batteries and don’t decompose at higher temperatures. Lithium-ion cells tend to contain highly flammable substances; if they’re damaged or overcharged, they can overheat uncontrollably in a thermal runaway. The overheating may result in smoke, fires, or even explosions.
LFP batteries provide the best thermal and chemical stability. In addition, because LFP has less energy density (in both volume and weight), and a higher cost per watt-hour than LCO, NCA, NMC, or LFP batteries, it’s ideal for applications that need high-power ratings, long cycle life, or elevated operating temperatures. Traditionally, there’s been very little overlap of LCO/NCA/NMC and LFP in their specific applications. The leading LFP cell manufacturers include BYD, CALB, and CATL.
NMC battery cells are displacing LFP cells in some applications due to increasing power ratings, high energy density, and lower cost per watt-hour. They’re also starting to replace LFP cells in high-power systems, such as power tools, batteries for material handling equipment, and powertrains for electric buses.
For each cell chemistry, segmentation exists within each category as battery manufacturers push their products to the high-energy or high-power segment of the market. We’re starting to see more overlap between high-power NMC and high-energy LFP cells. In many cases, there’s no longer a clearly superior cell chemistry for a specific set of performance requirements.
BSLBATT Lithium manufactures battery packs for many industrial applications, and the company generally uses LFP cells. Lithium iron phosphate is more compact and energy dense, making it an excellent choice for us in material handling applications, such as powering equipment like electric forklifts, walkie pallet jacks, and end riders.
Lithium nickel manganese cobalt oxide chemistries are very energy dense, which means they provide a higher level of performance, if the equipment is designed to support it. The high charge and discharge rates make it a more popular choice for electric vehicles, such as e-bikes, buses, cordless power tools and other electric power trains.
But a high discharge rate is only beneficial if you plan to use the equipment for shorter periods of time. Since most material handling equipment is used for an entire 8 to 10-hour shift, or even multiple shifts, the improved performance does not offer a benefit.
This type of battery chemistry uses a combination of nickel, manganese and cobalt for the cathode. Though the inclusion of nickel gives the cell high-specific energy, this also reduces its stability.
The inclusion of manganese, on the other hand, offers low internal resistance, but also features low specific energy. Combined, however, the chemistries work together to make this type of battery a suitable choice for certain types of equipment. The increased performance comes at a price…lithium nickel manganese cobalt oxide batteries have a lower thermal runaway temperature, meaning they are less safe than LFP.
To review: Lithium-ion cells packed in metal enclosures come in two shapes—cylindrical and prismatic.
The illustration compares the 18650 and 21700 cell sizes.
Cylindrical cells come in many formats, but traditionally, the most popular format for the LCO, NCA, and NMC battery cells has been the 18650. And when Panasonic partnered with Tesla to create a new EV battery, they developed the unique 21700 cell format.
Expanding the 18650 cell dimensions by several millimeters (Fig. 1) results in a 50% volumetric increase for the battery’s active material. This cell size is now currently supported by most leading NMC cell manufacturers. As a result, the 18650 and 21700 are the two most common formats for NMC chemistry.If you select a 18650 or 21700 cell to construct a NMC battery pack, finding an alternate cell with similar performance is assured given the standardization.
According to industry analysts, more than 2 billion cells based on the 21700 format were shipped in 2020, a 25% increase over the previous year. These types of cells also accounted for 24% of all cylindrical batteries shipped in 2020, other estimates show. The 26650 cell isn’t commonly paired with the NMC chemistry. Smaller prismatic NMC formats, such as the 103450 (10 × 34 × 50 mm), have fallen out of favor in recent years as lithium-polymer cells have become more popular.
For LFP cells, the 18650 and 26650 formats are common; both tend to be offered by leading LFP cell manufacturers (Fig. 2). That enables dual sourcing from competing cell manufacturers when choosing LFP cells for a battery pack. The 26650 format has been largely limited to the LFP cell chemistry. Large prismatic LFP cells, in the 50- to 100-Ah range, have risen in popularity over the last several years.
2. Performance characteristics of typical 18650 NMC and LFP cells.
Larger LFP prismatic formats are commonly used in electric vehicles or industrial equipment such as forklifts (Fig. 3). These batteries are classified as medium- or large-format, and demand very-high-power ratings. Unfortunately, standards are scarce for large-format prismatic LFP cells, so any cell selected for a battery pack will be single-sourced from a specific manufacturer.
3. This medium-format forklift battery is based on 100-Ah LFP cells.
The future of electric-powered products is already here. The advantages of switching from conventionally power sources are too good to ignore. As more and more industries and businesses become aware of the benefits of lithium-ion technology, the business decision to switch over is becoming a much easier one to make.
