Electrochemistry emerged as a separate field of chemistry after early scientists first started laying the groundwork for general electromagnetic theory and chemistry. Elements were discovered, conservation of mass and matter were accepted, electrostatic generators were built, and electrical detectors were invented all before scientists even started tinkering with electrochemistry. And the first steps were pretty gruesome. In 1800, an Italian doctor (Galvani) dissecting frogs was able to make dead muscles twitch by touching them with different metals connected to each other in series. A physics professor (Volta) disagreed on the mechanism and arranged stacks of different metals and brine-soaked paper to achieve similar results. This was the invention of the battery: the first device that turned chemical energy into electricity, but no one at the time knew how it worked. That didn't stop anyone from using it though; application outpacing understanding in the energy field has been the MO since the battery was first invented.
Electrochemistry got its first big scientific break from Michael Faraday in 1830s linking current (amount of electricity) and the amount of matter deposited during electroplating experiments. It took another 90 years and the framing of modern thermodynamics by Willard Gibbs before the groundwork of analytical electrochemistry was laid by Hermann Nernst relating voltage to chemical equilibrium. So only in the last decade of 1800 are we even able to discuss the describe the designed properties of a battery in simple terms of voltage and current.
So...electrochemistry took a while to get to a point where we can actually analyze it. So what? Shouldn't it have erupted in discovery after discovery since then? Not really. Most of the batteries we use today were invented long before anyone really understood what was going on. Even the modern lithium ion battery, invented in the 1980's, features a component called the "solid-electrolyte interface" (SEI) that sets the longevity and safety of lithium ion batteries, however scientists have only recently began to understand the structure and composition of it. In other words, the microns-thin layer that determines how long you can use a battery and whether or not it will burst into flames is the least understood part. There's almost too much that goes into the design of a practical battery not to take a trial-and-error approach. There's:
- The electrical potential of the positive and negative electrodes (sets the cell voltage)
- The chemical kinetics of the reactions at the positive and negative electrodes (helps determine maximum current)
- The structure of the electrodes (determined by the conductivity of the reactant species and the speed of the kinetics)
- The electrolyte composition and properties. This can be further broken down into:
- Operating pH (determines chemical compatibility with battery housing, electrodes; also determines prevalence of undesired side reactions)
- Conductivity (helps determine maximum current)
- Organic vs. Aqueous (determined by cell voltage, cost considerations, and storage reactions)
- The membrane separating the positive and negative sides of the battery (critical component, helps determine a lot of things)
- Cell durability
- Cell efficiency
- Maximum current draw
- Cost and manufacturability
- Operating temperature regimes
- Cell housing and architecture
- Sealed vs. Flow (flow batteries limited to liquid energy storage reactions)
- Bipolar vs. Monopolar (tradeoffs on manufacturability)
This is by no means an exhaustive list. To give an idea of how all these parameters fit together, I'll walk through an example in another post where we'll go from chemical fundamentals to full cell operation. During that exercise, it'll become pretty clear that we're lucky to have even what we have now given how easily things can go wrong.
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