ECN - March 2018

You gotta love Elon Musk—the man is everywhere. Current Musk projects include Tesla Motors, Power Wall, and SpaceX. Take a look at the drawing board, and things get interesting. Hyperloop promises to speed passengers from Los Angeles to San Francisco in 35 minutes; the Boring Company wants to cut costs of building tunnels by 75 percent, and recently made 20,000 flamethrowers available as a publicity stunt.

As ECN readers know very well, Tesla’s vehicles and Power Wall both rely on batteries to store and supply electrical energy. The market for batteries is on a roll as HEV/EV adoption rates continue to increase and utilities look for a way to balance supply and demand, as well as store the intermittent production from alternative energy sources such as photovoltaic (PV) cells and wind turbines.

According to GTM Research (Figure 1), the annual deployment for energy storage devices will total almost 1 GW in 2019; installations that capture energy from residential or commercial PV (solar) installations— commonly known as “behind-the-meter” deployments— will comprise half the annual market by 2021. The U.S. energy storage market will be worth an estimated $3.1 billion by 2022, a nine-fold increase from 2016 (and seven-fold from 2017).

Figure 1: U.S. annual energy storage deployment forecast 2012–2022. (Image Source: GTM)

The rise in battery-based energy storage is intimately linked with lithium-ion (Li-ion) chemistries: according to GTM analysts, they made up at least 97 percent of all storage capacity deployed in 2016. Li-ion also rules the roost in electric and hybrid vehicles, especially since Toyota, the last major holdout, switched most models of its flagship Prius hybrid from nickel-metal-hydride (NiMH) to Li-ion in the 2016 model year.

Reflecting the increase in demand, production volumes
have ramped up, while Li-ion battery cell prices have
fallen by about 60 percent in five years to around $139
per kilowatt-hour. Global battery manufacturing is
forecast to double from 2017 to 2021 and reach 278
GWh per year, accompanied by a further price reduction
of more than 40 percent.

Tesla is casting a long shadow over the Li-ion market. To protect against potential shortages, they’re moving to secure their own source of batteries. Their Gigafactory 1 in Sparks, NV, began production of Panasonic’s Li-ion design in 2017. When completed in 2020, the factory will produce 35 GWh of batteries yearly, primarily for in-house use. The company is already planning up to five Gigafactories.

Inside the Li-ion Battery

In spite of worldwide efforts to find better alternatives, why is Li-ion still slaying all comers?

One reason is the hurdles any challenger must surmount to make it to the finish line. There’s no shortage of candidates, and researchers regularly claim breakthroughs in battery chemistry, energy density, or charging time. So far, they’ve all been hobbled by some combination of high production costs, reliance on rare materials, problems with recycling or disposal, or limited number of charge/ discharge cycles.

Lithium (Li) is also a formidable opponent. With atomic number 3, it’s the lightest metal. Li has the greatest electrochemical potential and largest specific energy per weight, both highly desirable in a battery. A Li battery is non-rechargeable, while the pure metal is unstable, flammable, and potentially explosive when exposed to air or water, so research has concentrated on Li compounds that offer greater safety at the cost of slightly lower energy density.

Several Li compounds are in use for the positive electrode (cathode). Lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), and lithium cobalt oxide (LiCoO2) are three examples, each with characteristics optimized for different applications.

In current Li-ion batteries, the negative electrode (anode) is most commonly made of graphite.

The liquid electrolyte consists of Li salts in an organic solvent such as ethylene carbonate or dimethyl carbonate. During operation, Li-ions move from the anode to the cathode during discharging, and in the reverse direction during charging.