Metal Air, is it ready for Prime Time?
Imagine a world in the future where the boundaries between Energy & Matter are at best blurry and the infrastructure in our lives serves multiple purposes. Buildings that utilize the steel skeletons of the frame as inexpensive Iron electrodes with air that is ventilated throughout the building to provide both the HVAC necessities and the air for the Iron Air couple. A little fanciful maybe but certainly not outside the realms of possibility.
Zinc air was commercialized successfully in hearing aids in the 1980’s and sold in the hundreds of millions annually. Iron Air was developed by companies such as Westinghouse, Siemens and Swedish National Development Corp in the late 1970s in generator size batteries. Three (3) electron Aluminum Air has promised reusable batteries that could enable electric vehicle ranges of 1000 miles and unbelievably light Lithium Air, the holy grail of holy grails is too fantastical for words. These technologies have been the focus of many start- ups, company investments and government research grants over the last 20 years. None of the past programs have led to obvious success and it remains to be seen whether some of the current initiatives receiving attention will finally break the, “glass ceiling”. Big picture there are two big problems that must be solved for metal-air to be successful and the status of each is presented as follows:
1. Finding a good negative
However good the air electrode is, the metal-air cell and battery will always be limited by the negative and the negatives available have not until relatively recently had inspiring performance. Today, Zinc negative electrodes can confidently deliver over 1,000 cycles, Iron as a negative has had a resurgence and fuels cells with their hydrogen negative, have at least made steady progress even if they have disappointed versus their original billing. Zinc and Iron can meet the requirements. Aluminum and Lithium have a long way to go.
2. Solving the air conundrum
A metal-air battery needs oxygen to operate but the oxygen, water and carbon dioxide in the air will kill both electrodes given a chance. Carbonation of the electrolyte, air cathode flooding, winter sickness and negative electrode passivation and oxidation can all cause problems at the least and early battery failure most likely. It is difficult not to label metal-air batteries the, “Holy Grail” of the battery category. They have promised so much but for 30 years have fallen short of their promises. However just like when you begin to smell the salt in the air, feel the fresh breeze and see the seabirds you know you are near the sea, so too the signs for a viable, “Something-Air” battery can be seen in the progress that is now being made. The rest of this article explains the secret to this enigmatic Energy Storage System. Its prize will be worth the wait!
Not sure whether it is good protocol to talk about one’s experience in an article or Blog but before proceeding it is worthwhile talking a little about my qualifications.I led R&D efforts on Zinc Air for 10 years leading working on everything from small hearing air batteries to much larger Army portable telecommunication Systems. This work included a joint development program with AER Energy resources, a company that was attempting to develop Zinc Air solutions for devices such as cell phones, digital cameras. laptops and satellite tracking systems. I remain convinced that Zinc Air for sure and maybe Aluminum, Iron and Lithium will be a significant Energy Storage system in the future. Metal-Air’s inherent power limitations may not allow it to penetrate the EV market but it has every opportunity to win big in the on-grid and off-grid Energy storage market.
First of all some general comments. They are applied here to the “Air battery” opportunity but show me any battery success and these principles will certainly apply.
1. Keep it simple. Complicated solutions in batteries always fail or get beat by their simpler competition. For the foreseeable future this rules out Lithium Air and makes Aluminum Air at the least very difficult.
2. Never lose sight of the cost goal. Attempting solutions that do not obviously get below $100/kWh will not have a chance versus the incumbents, Lead Acid and Lithium Ion.
3. Don’t lose sight of the core attribute. I used to think batteries could be sold on a smorgas board of attributes but to connect with a killer App it has to be one and one only. For lead Acid it was cheap power. For lithium Ion it was light weight. For metal-air it is lowest cost Energy Storage.
4. The potential of Zinc Air will never be unlocked unless multiple innovations are combined into one battery solution. There is no single innovation that will succeed even though this is the way that many startups operate. A combination of inventions will be necessary, presumably preceded by the right cooperative agreements between multiple entities.
Now for some specifics applied to Zinc Air in particular but similar principles apply to the other Air electrode couples. Before detailing these it is important just to remind ourselves of the fundamentals. For a Zinc Air battery access of the Oxygen is necessary but the Oxygen in the wrong place and water and carbon dioxide in the air are battery killers.
Think on the Tornado! It has great and indeed dramatic power. It is not like the hurricanes that reek their devastation over a wide area. It is produced fundamentally by differences in pressure and heat and its devastation can appear surgical.
One moment the air can be still and the next hour it can be a raging storm. The key to the metal air battery is to think about it as trying to avoid a Tornado. The air must be there when it is needed and when it is not, the battery itself must exist in an air starved and therefore air safe situation. To achieve this we must start with the obvious, “It’s about the Oxygen, not the air” & the following principles must be applied:
5. A metal air battery will require next generation AER Energy resources technology. The air needs to be there when needed and not when it is not!
6. The Air cathode needs to employ the best technology available, conceivably combining the best of several. Electrode integrity, electronic conduction, hydrophobicity, surface adsorption and electro-activity all need to be in optimum balance for the Air cathode to perform as required in all circumstances.
7. Creative measures must be used to clean the air as much as possible. The AER diffusion technology , alone increases the shelf life of the battery by 25 X but for ultimate success another x 25 is required. Modern exchange resins, desiccants and selective membranes can be used to clean the air cost effectively centrally and this need not be very expensive once amortized over many kWh.
8. The metal air battery is an energy storage battery not a power battery. It will never be a power battery. Attempts to make it work in situations where power is required will lead to disappointment. If an application needs power a hybrid battery between metal-air and another electrochemical device is the obvious solution.
9. Electrodes in batteries need to be in intimate, consistent contact and in sealed systems it is very difficult to maintain the required stack integrity because of electrode swelling, gassing or sweating and electrolyte transport. Zinc Air in large systems needs cylindrical structure so that the simple mechanism of hoop strength can take care of this situation.
10. In Science fiction, Tornados might be produced or prevented by cleverly controlling the temperatures and pressures that produce them. Similarly, metal-air must be subject to very careful
temperature and pressure or air flow control if it is to work at all let alone effectively for many years. Diffusion gradients, internal resistance consistency, cell balancing challenges and clever charging algorithms all need to be included in the thought process and any development effort. However, as the world of computing and electronics continues to expand before our eyes the hardware and programming knowhow is surely now available to enable any battery to achieve its optimum performance.
Since its discovery in the 1800’s Zinc Air and its commercialization in the 1970’s, Zinc Air has continued to be a compelling opportunity. It is very easy to sell the proposition and I myself have done so many times. Pointing out the small amount of Zinc needed the hand then sweeps upwards and outwards to embrace the air in the room with the message, “I only need one electrode to capture active material and the other is all of the zero-cost air all around us!” Many companies have tried to crack metal-air for mainstream devices over the last 50 years and recently new start-ups have focused on the large-scale Energy Storage Market. At some point within the next ten years the key will be found and Zinc Air not looking back will quickly grow to rival Lead Acid and Lithium Ion.
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