Lithium-ion battery/es

Baterías de plomo ácido continúan siendo el estándar para los sistemas de almacenamiento de energía a nivel mundial debido a su bajo costo, confiabilidad y disponibilidad. Las baterías de ion de litio están comenzando a usarse con más frecuencia en los sistemas de almacenamiento de energía, ya que ofrecen varias características atractivas para sistemas FV autónomos. Existe una variedad de diferentes químicas de ion de litio, pero hay dos en particular que han surgido como las tecnologías más populares para sistemas FV autónomos: litio, hierro y fosfato (LFP) y litio, níquel, manganeso y cobalto (NMC).

Las baterías de ion de litio se componen de muchas celdas pequeñas que están cableadas en serie y en paralelo para lograr el voltaje nominal deseado. Estas celdas son muy sensibles a la sobrecarga y, por lo tanto, requieren un sistema de gestión de batería (SGB) o (BMS en íngles) para garantizar una carga adecuada de la batería. La carga incorrecta no solo puede dañar irreparablemente las baterías, sino que también puede provocar un evento de fuga térmica con baterías NMC en el que la temperatura de una batería ya no se puede controlar y aumenta hasta el punto de que el equipo se daña o se provoca un incendio.

El diseño de las baterías de iones de litio y la presencia de un sistema SGB significa que las baterías están diseñadas para funcionar a un voltaje nominal establecido y no están diseñadas para conectarse en serie como se hace con las baterías de plomo ácido. Se venden en voltajes nominales que se pueden cablear en paralelo para lograr la capacidad Ah o kWh deseada. Una de las ventajas de los sistemas BMS que acompañan a cada batería es que se garantiza una carga adecuada para todas las baterías conectadas en paralelo, lo que significa que, por lo general, no hay un límite en la cantidad de baterías que se pueden poner en paralelo como ocurre con las baterías de plomo ácido (es mejor limitar la cantidad de baterías de plomo-ácido en paralelo a no más de tres cadenas para garantizar una carga adecuada).

Lithium ion battery types

Diagramas que comparan diferentes tipos de baterías de iones de litio. El anillo más externo es la calificación o rendimiento más alto. El anillo más interno es la calificación o rendimiento más bajo.
(1) Densidad de energía (2) Densidad de potencia (3) Seguridad (4) Toxicidad (5) Vida útil (6) Costo

Lithium iron phosphate (LFP) and Lithium nickel manganese cobalt (NMC) each have distinct advantages that lend themselves to different applications.

LFP

LFP batteries have emerged as the preferred technology for stand-alone applications as they offer several advantages when compared to NMC batteries: a longer cycle life, a lower price point per kWh, a less toxic chemistry, and a lower probability of thermal runaway events. The characteristics of LFP batteries enable manufacturers to build smaller batteries that can function as drop-in replacements for lead acid batteries in many different systems.

NMC

The main advantage of NMC batteries is that they have a higher energy density (can store more energy for the same volume/weight) and can function with higher charge/discharge currents. NMC batteries are typically found in larger integrated systems like those built by LG Chem and Tesla.

Compatibility with other equipment

It is important to make sure that any equipment used with lithium-ion batteries is compatible with them. Many have different parameters/voltages than lead acid batteries that will require additional programming. These parameters vary significantly - consult the manual or manufacturer of any battery being considered.

Battery storage

Lithium-ion batteries often come with enclosures or racks provided by the manufacturer. The manual and manufacturer should be consulted to determine the appropriate means of storage. They should be stored in an enclosure or room that prevents unauthorized access via a lock. If being installed in a harsh environment, it is ideal if they are kept in a climate-controlled environment. They cannot be charged below 0°C.

Safety

Lithium-ion batteries are always sealed and do not, except during an a thermal runaway event or an accident, present a risk for exposure to hazardous chemicals. In the case of electrical hazards, they still carry risks of arc flashes and a potential for shocks with higher voltage systems, but they are also typically safer than lead acid batteries when it comes to electrical hazards as they often have additional safety measures provided by the battery management system, overcurrent protection devices, or an integrated disconnect. These measures work to ensure that the battery does not provide current unless properly connected and activated by the installer.

Recyclability

Recycling lithium-ion batteries can be somewhat of a challenge when compared to lead acid batteries which have a global recycling network. This is partly because many of materials that they contain are not as valuable as lead, but also because the recycling processes are more complicated which has limited the number of facilities globally that are capable of handling them. The appropriate way to recycle a battery depends upon the manufacturer and its chemistry - they manufacturer will be the best resource for determining how to dispose of batteries. Many LFP batteries contain no hazardous chemicals, which is a distinct advantage over lead acid batteries and NMC batteries.

Comparison with lead acid batteries

Lithium-ion batteries have both advantages and disadvantages with compared with lead acid batteries.

Advantages:

• Higher energy density. They can store significantly more energy in the same space/weight.
• Longer cycle life. They can provide 2-3 times as many cycles as lead acid batteries.
• Can accept a high charge current until nearly completely full - no absorption phase is required. This allows allows more rapid and efficient charging during the limited daylight hours when the PV source is operating or when running a generator.
• Higher round trip efficiency. 95-98% as compared to 80-90% efficiency for lead acid batteries.
• Higher depth of discharge. 80-100% with each cycle is possible as compared to recommended maximum of 50% with lead acid batteries.
• Voltage is not very responsive to temperature, which means that lithium ion batteries perform better in warm temperatures. Temperature compensated charging is not required.

Disadvantages:

• Higher upfront investment. Although the cost per cycle of some lithium-ion energy storage systems is comparable to that of lead acid batteries.
• Very sensitive to over-discharging and over-charging. The amount of current that can be inputted/outputted is limited and if exceeded can irreparably damage the batteries.
• Require a battery management system.
• Risk of thermal runaway events.
• Far more sensitive to low temperatures. Cannot be charged below 0°C.
• Limited availability.
• Limited compatible equipment availability.

Notes/references

Hydrowires - Energy Storage Technology and Cost Characterization Report
Chemical and Engineering News - It’s time to get serious about recycling lithium-ion batteries
Isidor Buchman - Batteries in a Portable World
Thomas Reddy - Linden's Handbook of Batteries, 4th Edition