Lithium Batteries and Storage

Lithium Ion (LI-ION) Batteries

Executive Summary

In 1991 Sony and Asahi Kasei released the first commercial lithium-ion battery. The first batteries were used for consumer products and now building on the success of these lithium-ion (Li-ion) batteries, many companies are developing larger-format cells for use in energy-storage applications. Many also expect there to be significant synergies with the emergence of electric vehicles (EVs) powered by Li-ion batteries. The flexibility of Li-ion technology in EV applications, from small high-power batteries for power buffering in hybrids, to medium-power batteries providing both electric-only range and power buffering in plug-in hybrids, to high-energy batteries in electric-only vehicles, has similar value in energy storage.

Li-ion batteries have been deployed in a wide range of energy-storage applications, ranging from energy-type batteries of a few kilowatt-hours in residential systems with rooftop photovoltaic arrays to multi-megawatt containerized batteries for the provision of grid ancillary services.


The term “lithium-ion” refers not to a single electrochemical couple but to a wide array of different chemistries, all of which are characterized by the transfer of lithium ions between the electrodes during the charge and discharge reactions. Li-ion cells do not contain metallic lithium; rather, the ions are inserted into the structure of other materials, such as lithiated metal oxides or phosphates in the positive electrode (cathode) and carbon (typically graphite) or lithium titanate in the negative (anode).

The term “lithium polymer” (or more correctly, lithium-ion polymer) refers to a Li-ion design in which the electrodes are bonded together by a porous polymer matrix. Liquid electrolyteis infused into the porous matrix and becomes immobilized, allowing the electrode stacks to be assembled into foil “pouches” that provide geometric flexibility and improved energy density compared to cylindrical cells. However, such advantages are less significant as the cells are scaled up to larger capacities. (Note that there are also “lithium metal polymer” technologies, in which metallic lithium negative is implemented with a conductive polymer to make a solid-state battery system. Such technologies do not fall under the Li-ion umbrella and have not yet been successfully deployed in energy-storage applications.)

Technologies with lithiated metal oxide positives and carbon negatives have high cell voltages (typically 3.6 V to 3.7 V) and correspondingly high energy density. These technologies have widely differing life and safety characteristics. Cells with positive materials based on lithium iron phosphate are inherently safer than their metal oxide/carbon counterparts but the voltage is lower (around 3.2 V), as is the energy density. Designs with lithiated metal oxide positives and lithium titanate negatives have the lowest voltage (around 2.5 V) and low energy density but have much higher power capability and safety advantages.

Li-ion cells may be produced in cylindrical or prismatic (rectangular) format. These cells are then typically built into multi-cell modules in series/parallel arrays, and the modules are connected together to form a battery string at the required voltage, with each string being controlled by a battery management system. Electronic subsystems are an important feature for Li-ion batteries, which lack the capability of aqueous technologies (e.g. lead-acid batteries) to dissipate overcharge energy. Safety characteristics of Li-ion batteries are ultimately determined by the attributes of system design, including mechanical and thermal characteristics, electronics and communications, and control algorithms, regardless of electrochemistry.


The World’s Largest Lithium-Ion Energy Storage Facility

The 30 megawatt (MW) energy storage plant at Escondido, CA, has a capacity of up to 120 megawatt-hours of energy. It could serve 20,000 customers for 4 hours.

A smaller, 7.5 MW installation was erected in El Cajon.

“On a day (like Friday), which is nice and sunny, but also cool, demands for energy in the middle of the day aren’t very high but production is. So we’d be storing solar in the day and releasing it at 6:00–7:00 tonight after everyone’s home from work, and school, and home with their families. It’s a tool that we can use to make the integration of solar and wind much more reliable and better matched to the times when our customers need it most,” said Josh Gerber, Project Director SDG&E.

“Even though this is the largest energy storage project in the world, it came online in about six months. So it is one of the quickest installed projects in the world as well,” said John Zahurancik, AES Energy Storage president.

“These projects affirm our commitment to deliver clean energy to customers and to provide a more reliable power supply to our electric grid when it is most needed,” said SDG&E’s president, Scott Drury.

165 MW Of Energy Storage By 2020

These two plants are the first steps in  SDG&E’s compliance with the CPUC regulations that it must procure a total of 165 MW of energy storage by 2020, and it must be operational by 2024.

SDG&E intends to develop, or interconnect, more than 330 MW of energy storage by 2030.

Photo Credits: 

  1. SDG&E Escondido Battery Energy Storage Facility. Courtesy SDG&E.
  2. After SDG&E President Scotty Drury (l) flipped a symbolic battery storage switch. With Drury is (l to r) CPUC President Michael Picker, AES President John Zahurancik, and Escondido Mayor Sam Abed. Courtesy SDG&E.
  3. SDG&E Escondido Battery Energy Storage Facility. Courtesy SDG&E.