Understanding Advanced Batteries and Energy Storage – Part 2
To put it bluntly, batteries suck!
We have a love-hate relationship with them. We can’t imagine life without batteries but we’re rarely happy with them because they invariably need to be recharged or replaced at the worst possible moment. There’s a reason that “damned” is the attributive adjective most commonly associated with the noun. The best summation I’ve ever heard came from a PhD electrochemist who said, “Batteries are a grudge purchase.”
My love-hate relationship with batteries runs deeper than most. From 2004 through 2007, I worked as legal counsel for and served as chairman of a public R&D stage battery company. Since 2013, I’ve been an officer and director of a private company that’s developing a unique hybrid drivetrain for heavy trucks and struggling to find a battery that can handle the drivetrain’s power profile. Between the two battery-related jobs I blogged about investing in energy storage with less than gratifying results. My bearish predictions of likely business failure were usually right but my bullish predictions were frequently wrong. Energy storage is a very tough sector to forecast if you don’t have a flawless crystal ball.
Since my record as a stock picker is spotty at best and my goal in writing for InvestorIntel is to help serious investors understand the energy storage space, I’ll generally avoid the temptation to mention specific companies unless they’re particularly apt examples of an important point.
Energy vs. power
While most people use the terms interchangeably, energy and power are not the same thing. In physics, the term “energy” is used to describe the total capacity to perform work while the term “power” is used to describe the rate at which work can be performed. When you’re talking about electricity, power is measured in watts and thousand unit multiples (kilowatt, megawatt, gigawatt and terawatt) while energy is measured in watt-hours and thousand unit multiples.
Other energy and power measurements that frequently crop up in battery discussions include “specific energy,” measured in watt-hours per kilogram (wh/kg), “energy density” measured in watt-hours per liter (wh/l), and “specific power,” measured in watts per kilogram (w/kg).
If you think of batteries as bottles for electricity, “specific energy” describes the bottle’s capacity and “specific power” describes the size of the bottle’s mouth.
While, batteries can be optimized for either energy or power, that process usually involves trade-offs where you sacrifice energy for power or sacrifice power for energy. Comparisons that don’t describe both energy and power are usually incomplete, and so are cost metrics like $/kWh. If you want to understand a particular battery’s value proposition you need all the numbers.
Chemistry in a can
Batteries are essentially chemistry in a can. To build an electrochemical cell, you start with an empty container, insert two electrodes that are isolated by porous separators and then soak all the components with an electrolyte that serves two primary functions:
promoting changes in the molecular state of chemically active materials; and
promoting the movement of ions between electrodes.
In all cases, the mass of chemically active material you can fit into a particular container, after leaving room for current collectors, separators and electrolyte, limits the energy you can take out of that container. While electrons moving about a circuit board have no appreciable size or mass, the active molecules inside a battery are both large and heavy. As a result, every electrochemical cell stores a limited amount of energy and fades like a wind-up toy as active molecules release the stored energy. In most cases, electrochemical cells discharge faster than they recharge. Since electrochemical reactions are never 100% reversible, all batteries suffer a small but permanent capacity loss with each charge-discharge cycle. When the capacity loss becomes too great, a new battery is the only option.
Batteries hate hard work
The capacity of a battery is calculated by multiplying its voltage by its amp-hour rating. So a 10-volt battery with a 100 amp-hour rating will have a capacity of 1,000 wh, or 1 kWh.
Batteries deliver their best energy efficiency, performance and cycle life in applications that offer stable charge and discharge conditions in ambient temperatures that optimize chemical reactions. The poster child application is a smart phone that discharges the battery over a period of 12 to 16 hours, recharges the battery overnight and does most of its work at room temperature.