The Difference Between Capacitors Supercapacitors And Batteries

[Music] hi sir I've been asked a number of times actually to talk about the difference between capacitors super capacitors and batteries and so I'm going to do that in this video and if that isn't your thing then probably the best thing to do is not watch the video if it is what you're interested in then I'm going to go into it a little bit and the problem with it though is that the answer you're looking for probably isn't the answer I'm going to give and that's a shame because the answer a lot of people expect is that a capacitor is this a super capacitor is this and a battery is this done and that would be lovely if that's the heavy amount once but because it isn't the way the world was well a little box that we call Sabaton capacitor super capacitor and battery are in fact categories to put things into a jerem aid our understanding now it's important to categorize because categorization is the method by which we understand the world and create a map of it and then move through that world in a predictive kind of way so categorization is really important but what tends to happen then is we fix those categories as being immutable and of course they're not it's the chair table problem we all understand what the category chair is and I'm sitting in the chair right now and I hear it's got a back and I know it's a chair and I know how to use it but there is a degree of channeis about that chair that makes it a chair and if I change that degree we get to a gray edge where the chair is difficult to recognize as a chair well maybe we remove the back we'd start calling it a stool what about if I put my coffee cup on it is it a stool or a table at what point does it transition between stool and table and become a whole new category now to talk about line that seems a little trivial and I agree it is but it also illustrates the point that I'm trying to make that categories are fine to aid of understanding but become an error when you think that that's all there are now there's lots of ways of understanding what a capacitor supercluster of battery is and there's lots of ways of defining them so that we can talk about them and understand which box they fit in now one way is by definition we can say that a capacitor is such a beast and if it were not that beast it would not be a capacitor that's way of doing it and one way is to look at the function that it performs if in a capacitor in a circuit is acting as a smoothing filter it's a capacitor if it's in an energy storage and its power dense it's a capacitor so we can define it by its function we could talk about it by structure where we have two plates in a field in between them there are lots of ways of actually looking at that to enable the understanding the worst way in my mind anyway is to define it and say strictly that's what it is and it can't be that if it's not that thing that I think there's an extraordinarily narrow view and rather than helping you understand actually just fixes your view and prevents understanding so I tend to shy away very much from definition I tend to be a functionalist I tend to be structuralist I certainly don't define things that strictly and then stay with that definition now obviously we're on a curve of people so it doesn't really matter what you say somebody somewhere is gonna disagree with you and some people disagree rather loudly because they think that they're louder they shout the more truth they must be shouting well it's not me and I don't have much time for it and you know that's what you think I don't really worry about it anyway because that's you and not me but if that's what you think you're probably not going to like what it is that I'm saying and that's okay thumbs be down if we think about the structure of something and that's what we'll talk about to a degree then we can think of a capacitor as being the electrostatic equivalent of a magnet if we get a two magnets and we have them facing north and south they'll pull towards each other because there's a field in between them slopping around I'll push away because they have the same blank field and when we look at those magnets and feel that force there's nothing between them which is part of what makes it magical now we can see that if we sprinkle some iron filings there then the iron will rotate to line up with the field giving us a second hand view of what that mystical force is now capacitors are very much the same this justice an electrical phenomenon is opposed to a magnetic phenomenon where we get two plates when we put a charge on it we actually create a field that juices the opposite charge on the plate so we get two plates of metal and they'll have an opposite charge and in between them is a field now that field will have an effect on any material that's been between them what they'll do is cause the molecules to line up and when they feel this turned off those molecules will unlined releasing energy and that's what the dialectic constant is you can think of it a bit like a water pipe with a balloon in it if we have a pipe and put a balloon and pour some water in the balloon will pop out and it bulge out into the other side of the pipe storing the energy we then stop putting water and they come back out again the balloon will tighten up and the water will be forced down of course the strength of which that water is forced out will depend on what that balloon is made of and it's very similar with capacitors they have a proper materials have a property called the dialectic constant which if you like in the same way is like the strength of the balloon it has a strength of its ability to deal with that field and stall the energy that that field is creating now on something like polyethylene that field is around about 4 it's not it's just to give you an illustration of the differences between these things maybe use something like to turn em down side so that's about 250 if we use something like barium titanate that's something like 150 thousand now the strength of a capacitor is related to the plate surface area the distance they are apart and that material in between which is called the dialectic constant we multiply those old together and we'll get a value for the capacitor so clearly that material can have a big impact on the capacitor and that makes sense when you think about the balloon that we just talked about if that balloon is a metaphore pretty tough stuff takes a bit of force to get in there when it springs back it's gonna shoot a lot back out again so it's obvious that those kind of materials would have a big difference and the energy that's stored in a device like that that consumption of parallel plates was essential and fundamental to understanding what a capacitor at that end was now that was great for a very long time until we came up with super capacitors which are a real problem of course because they store an awful lot more energy than they should the reason they do that is they have an enormous surface area now you can do that with ordinary capacitors if we take just a standard capacitor which is a bit of metal on something like tantalum oxide or something like that they'll have a capacitance the nearer we can get those pledged to each other the higher the capacitance is going to go because it's divided by the distance then more than just lower the distance the higher the capacitance when we look at an electrolytic capacitor the electrolytic capacitor is basically an aluminium sheet and then dialectic is a bit of aluminium oxide the other pledge is in fact the electrolyte is just collected by a and yet another aluminium plate but the plate is the electrolyte that thickness of the aluminium oxide that grows our shrinks as you apply a current is the dialectic that is reducing or increasing with the distance between the two plates that is one piece of aluminium and the electrode and so that distance can get very small indeed and so electrolytic capacitors can store an awful lot of energies far more than a solid-state capacitor they are polarized of course because we need to maintain the aluminium oxide layer with that movement from a strict material in terms of the two layers of plates are now a sudden electrolytic material is beginning that change over from what a capacitor was so if we define a capacitors being to placed as something in between them then the electrolytic capacitor actually stretches that a little bit the plate has to be considered to be the electrolyte so we're stretching that definition a little bit when we move to something like the super capacitor then the large surface area afforded by the carbon comes a very common thing for it you can use other materials but carbon sorry common creates an absorbed layer of ions on the surface of the carbon let's say for instance it has a negative charge and we get an air of positive charges on it obviously we now have a positive layer and that will attract them there of negative charges so we get two Raja's now two layers of charged ions with the separation between them and we have what looks like a traditional capacitor that is - pledged charge between the field in between that double layer incidentally is called the Helmholtz layer and it will continue to grow Plus 9 is plus minus plus minus until the dynamics of the system overwhelm the ability for those layers to grow the length of those layers is actually called the Debye length so they will continue to grow here you should be able to see that that definition is being stretched yet again because now instead of just having two passive components that is two plates in relationship to each other we actually have a very strongly active component now now that moon and that system actually consists of moving ions laying up in layers because if we do now we can also start to introduce other effects so the surface of the carbon for instance will have an impact on the ability of that surface to attract the positive ions so changing that surface will change the number of arms are attracted to it and therefore the energy that's going to be stored in that device but have we strictly just done that by applying a feeler I've charged to one surface and creating a field or have we introduced an element of electro chemistry in there well of course we've introduced an element of electro chemistry once you introduce an element of electro chemistry you'd then begin to move towards batteries because batteries are electrochemical systems traditionally of course they were just redox system this reduction oxidation but there were electrochemical systems and here we have a device that is kind of half a battery and half a capacitor because we've got that layer that we were looking at when we looked at the original capacitor but now we've got an electrochemical element to it and yet there is no actual reaction there's just an electrochemical contribution there's no real reaction going on there so it's not a battery but equally there is an electrochemical to it so it's not a capacitor so we started defining this mid stage point where it stores a lot of energy but sorry my mistake it stores a lot of power but not a lot of energy so we have this device in the middle which is very power dense and with something called those super capacitors now one of the things that helped differentiate a super capacitor from the battery is the power density super capacitors aren't very energy dense they can't store a lot of energy but they're extremely power dance between said because they are separated only in bound the inter atomic distance of the plus and the minus ion that feel the collapse very rapidly and it can deliver the energy very rapidly indeed and and power is energy over time so it's time to create these devices but of course people just can't resist on fiddling on with things no fiddling with things and start doing other stuff to it again you start to change it so looking at the original surface of carbon then modifying it so it did that job better and creating points of active site and introducing electro chemical element was only one aspect of what we actually started to do we also started to look at the electrolyte could the electrolyte they enabled to store more energy and of course it can because we're looking at electron transfer so if we actually absorb an ion and change the electrons in that ion then there is a faraday reaction going on now it may be very short term there may be a very short distance living at last a long time but there is an element of strong element to Faraday reaction not because it's such transient reaction is called a pseudo faraday reaction as faraday reactions occur at the surface through the iron on the electrolyte which you can select and so are we actually introducing a redox behavior well yes we are and it's like it's pushing it towards the battery end of things and this begins to get us a bit more confused because now we're moving this capacitive device along mask towards a battery line device son it becomes questionable about whether that chair is a table or not the other side of things of course is that batteries for a very long time we're only one thing which is great because it was easy to understand them there were a tub with two bucket both elements in there we had an electrochemical reaction a redox reaction and we got energy out awesome that's a battery because we then came up with other mechanisms for storing energy so when you think about a traditional battery of that turn type you're thinking of lead acid batteries when you think of a lithium-ion battery actually that's not what's going on what goes on lithium ion battery is that the islands are shuttled between the cathode and the anode that have different energy stairs depending on where they're those ions sit if you think about what it is then you tend to have a graphite layer and then another layer of material on the other side it's it's seriously something like lithium phosphate or something like that the electrolyte tends to be in the lithium tetrafluoroborate for example and so the lithium ion can shuttle across between those two materials and be hosted by those materials and sitting in as galleries of the graphite then you start to ask yourself actually if that battery is doing that and we've just talked about super capacitors having sudo Faraday at reaction sites on their surfaces and here we have a battery with a Faraday reaction site on its surface where's the different stab it and it has become a very gray area and where that difference actually exists so it becomes difficult really to start to separate these things out when you start to look at the transitions from one point to the other point now we talked to a little bit there about how that energy is stored so in a battery like the lithium-ion batteries of America referred to as a rocking-chair battery because the island is rocks between the two it's just a man mechanism for storage and for storage of energy I tend to think about these things in terms of the storage of energy but that's because that's my particular interest that's what I want to do I'm very interested in how much energy can store and how quickly can deliver that energy that is how much power is got so I'm tend to see all of these devices as energy storage devices along a steamer as opposed to being a specific thing that does only a certain job but that's my own limitation that's because I'm only interested in that one job to a frequency dependency for instance is of no interest to me at all there's long as the thinkin cycle I don't care if the supply is you have a couple of gigahertz but then I don't design circuits for mobile phones so frequency dependency is just not an issue for me there are plenty of people who do in which case they would head the way I see this because to them a capacitor is a specific thing doing a specific job and that's good because to me it's just the same it's just a job that I'm interested in is energy storage so I don't really differentiate much between those things only in terms of their ability to store and release that energy under certain conditions to me a battery is something they'll store an awful lot of energy and release it slowly the super capacitor is something that won't still that much energy but will release it very quickly a capacitor obviously stores next to none but the ability to get that energy out is almost instantaneous so I'm only interested in that aspect of it and as I said that's my limitation for those things in general terms of course the function a capacitor needs to perform within a circuit is part of how you want to understand that capacitor now I don't really want to understand it and electronic terms I don't know that much about it if I'm brutally honest I want to understand it in terms of storage in its chemistry and as I'm a chemist and that's what I intend that's what I know about and money's actually I've focused on so you have a different functional view and you want to challenge what it is that I'm saying that's that's fine it just means that your function that you want to perform is different from the function that I want to perform to give me so thinking about the difference between capacitor super capacitors and batteries we've introduced quite a lot of ideas one thing is you need to think about the function and define what it is that you're asking in terms of that so why are you asking that question what job do you want to do and if you don't like me and you want the job to be energy storage then you're going to be driven down in one route of understanding the difference between these things if you have a different function in mind you're going to want enough another understanding of the function of these things so the function you want are they the job you wanted to do should impact heavily on your understanding of the differences between them the structures that we've talked about also should heavily impact how it is you think about it whether it's something to do with the parallel plate formation or is something to do with a chemical reaction those are going to help define what makes a device a particular device so I'd say I don't think it was a particularly clear-cut answer because I don't think there is a particularly clear Chi answer but I do hope it helped to some degree in understanding where it is so where these things sit on that schema but when they sit on that schema has a great deal unfortunately to do with you and and what it is you want to understand about them and that's obviously something that frequently escapes people because like to say a lot of people want the answer it's this it's this it's this that's the truth deal with it unfortunately of course that isn't the way things are lit it's not the way I see things I see things as being driven by what you want to do with it and what understanding you need to have of it in order to be able to define it and use it and develop it it's not very satisfying but it's the best answer I can give so I hope it was of interest I hope it did help and didn't just confuse and thank you very much for watching

Channel: Robert Murray-Smith

Views: 18,374

Rating: 4.9410319 out of 5

Keywords: supercapacitors, battery, capacitor, robert, fwg, murray-smith, chemistry, batteries, physics, energy, storage, science, lesson, education, technology

Id: lu0PMQW53ds

Length: 19min 47sec (1187 seconds)

Published: Thu Jul 09 2020