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Posts Tagged ‘lithium ion batteries

on the explosion of battery research – part one, some basic electrical concepts, and something about solid state batteries…

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just another type of battery technology not mentioned in this post

Okay I was going to write about gas prices in my next post but I’ve been side-tracked by the subject of batteries. Truth to tell, I’ve become mildly addicted to battery videos. So much seems to be happening in this field that it’s definitely affecting my neurotransmission.

Last post, I gave a brief overview of how lithium ion batteries work in general, and I made mention of the variety of materials used. What I’ve been learning over the past few days is that there’s an explosion of research into these materials as teams around the world compete to develop the next generation of batteries, sometimes called super-batteries just for added exhilaration. The key factors in the hunt for improvements are energy density (more energy for less volume), safety and cost.

To take an example, in this video describing one company’s production of lithium-ion batteries for electric and hybrid vehicles, four elements are mentioned – lithium, for the anode, a metallic oxide for the cathode, a dry solid polymer electrolyte and a metallic current collector. This is confusing. In other videos the current collectors are made from two different metals but there’s no mention of this here. Also in other videos, such as this one, the anode is made from layered graphite and the cathode is made from a lithium-based metallic oxide. More importantly, I was shocked to hear of the electrolyte material as I thought that solid electrolytes were still at the experimental stage. I’m on a steep and jagged learning curve. Fact is, I’ve had a mental block about electricity since high school science classes, and when I watch geeky home-made videos talking of volts, amps and watts I have no trouble thinking of Alessandro Volta, James Watt and André-Marie Ampère, but I have no idea of what these units actually measure. So I’m going to begin by explaining some basic concepts for my own sake.

Amps

Metals are different from other materials in that electrons, those negatively-charged sub-atomic particles that buzz around the nucleus, are able to move between atoms. The best metals in this regard, such as copper, are described as conductors. However, like-charged electrons repel each other so if you apply a force which pushes electrons in a particular direction, they will displace other electrons, creating a near-lightspeed flow which we call an electrical current. An amp is simply a measure of electron flow in a current, 1 ampere being 6.24 x 10¹8 (that’s the power of eighteen) per second. Two amps is twice that, and so on. This useful video provides info on a spectrum of currents, from the tiny ones in our mobile phone antennae to the very powerful ones in bolts of lightning. We use batteries to create this above-mentioned force. Connecting a battery to, say, a copper wire attached to a light bulb causes the current to flow to the bulb – a transfer of energy. Inserting a switch cuts off and reconnects the circuit. Fuses work in a similar way. Fuses are rated at a particular ampage, and if the current is too high, the fuse will melt, breaking the circuit. The battery’s negative electrode, or anode, drives the current, repelling electrons and creating a cascade effect through the wire, though I’m still not sure how that happens (perhaps I’ll find out when I look at voltage or something).

Volts

So, yes, volts are what push electrons around in an electric current. So a voltage source, such as a battery or an adjustable power supply, as in this video, produces a measurable force which applied to a conductor creates a current measurable in amps. The video also points out that voltage can be used as a signal, representing data – a whole other realm of technology. So to understand how voltage does what it does, we need to know what it is. It’s the product of a chemical reaction inside the battery, and it’s defined technically as a difference in electrical potential energy, per unit of charge, between two points. Potential energy is defined as ‘the potential to do work’, and that’s what a battery has. Energy – the ability to do work – is a scientific concept, which we measure in joules. A battery has electrical potential energy, as result of the chemical reactions going on inside it (or the potential chemical reactions? I’m not sure). A unit of charge is called a coulomb. One amp of current is equal to one coulomb of charge flowing per second. This is where it starts to get like electrickery for me, so I’ll quote directly from the video:

When we talk about electrical potential energy per unit of charge, we mean that a certain number of joules of energy are being transferred for every unit of charge that flows.

So apparently, with a 1.5 volt battery (and I note that’s your standard AA and AAA batteries), for every coulomb of charge that flows, 1.5 joules of energy are transferred. That is, 1.5 joules of chemical energy are being converted to electrical potential energy (I’m writing this but I don’t really get it). This is called ‘voltage’. So for every coulomb’s worth of electrons flowing, 1.5 joules of energy are produced and carried to the light bulb (or whatever), in that case producing light and heat. So the key is, one volt equals one joule per coulomb, four volts equals 4 joules per coulomb… Now, it’s a multiplication thing. In the adjustable power supply shown in the video, one volt (or joule per coulomb) produced 1.8 amps of current (1.8 coulombs per second). For every coulomb, a joule of energy is transferred, so in this case 1 x 1.8 joules of energy are being transferred every second. If the voltage is pushed up to two (2 joules per coulomb), it produces around 2 amps of current, so that’s 2 x 2 joules per second. Get it? So a 1.5 volt battery indicates that there’s a difference in electrical potential energy of 1.5 volts between the negative and positive terminals of the battery.

Watts

A watt is a unit of power, and it’s measured in joules per second. One watt equals one joule per second. So in the previous example, if 2 volts of pressure creates 2 amps of current, the result is that four watts of power are produced (voltage x current = power). So to produce a certain quantity of power, you can vary the voltage and the current, as long as the multiplied result is the same. For example, highly efficient LED lighting can draw more power from less voltage, and produces more light per watt (incandescent bulbs waste more energy in heat).

Ohms and Ohm’s law

The flow of electrons, the current, through a wire, may sometimes be too much to power a device safely, so we need a way to control the flow. We use resistors for this. In fact everything, including highly conductive copper, has resistance. The atoms in the copper vibrate slightly, hindering the flow and producing heat. Metals just happen to have less resistance than other materials. Resistance is measured in ohms (Ω). Less than one Ω would be a very low resistance. A mega-ohm (1 million Ω) would mean a very poor conductor. Using resistors with particular resistance values allows you to control the current flow. The mathematical relations between resistance, voltage and current are expressed in Ohm’s law, V = I x R, or R = V/I, or I = V/R (I being the current in amps). Thus, if you have a voltage (V) of 10, and you want to limit the current (I) to 10 milli-amps (10mA, or .01A), you would require a value for R of 1,000Ω. You can, of course, buy resistors of various values if you want to experiment with electrical circuitry, or for other reasons.

That’s enough about electricity in general for now, though I intend to continue to educate myself little by little on this vital subject. Let’s return now to the lithium-ion battery, which has so revolutionised modern technology. Its co-inventor, John Goodenough, in his nineties, has led a team which has apparently produced a new battery that is a great improvement on ole dendrite-ridden lithium-ion shite. These dendrites appear when the Li-ion batteries are charged too quickly. They’re strandy things that make their way through the liquid electrolyte and can cause a short-circuit. Goodenough has been working with Helena Braga, who has developed a solid glass electrolyte which has eliminated the dendrite problem. Further, they’ve replaced or at least modified the lithium metal oxide and the porous carbon electrodes with readily available sodium, and apparently they’re using much the same material for the cathode as the anode, which doesn’t make sense to many experts. Yet apparently it works, due to the use of glass, and only needs to be scaled up by industry, according to Braga. It promises to be cheaper, safer, faster-charging, more temperature-resistant and more energy dense than anything that has gone before. We’ll have to wait a while, though, to see what peer reviewers think, and how industry responds.

Now, I’ve just heard something about super-capacitors, which I suppose I’ll have to follow up on. And I’m betting there’re more surprises lurking in labs around the world…

 

 

Written by stewart henderson

July 29, 2017 at 4:00 pm

How will the super-duper Tesla battery work? And more on the price of electricity

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Image: Thermo Fisher Scientific Inc.

I received an email the other day from the Australia Insitute. I don’t know how that happened, I’ve never heard of the organisation. Apparently it’s Australia’s most influential progressive think-tank (self-described) and apparently I subscribed to it recently while in a barely conscious state. All good.

Anyway the topic was timely: ‘Rising Energy Bills: Blame Gas’.

In a very recent post I quoted from a few apparently reliable sources on the reason for South Australia’s very high electricity prices. Unfortunately there wasn’t too much agreement among them, though at least none of them blamed renewable energy. But neither did any of them blame gas, though one did point a finger at wholesale pricing. The Australia Institute’s email put it thus:

Yesterday, we released the latest Electricity Update of the National Energy Emissions Audit for July 2017. The report revealed a stunning correlation between domestic electricity prices and gas prices — particularly in South Australia — despite gas making up only 10 percent of electricity generation.

So this is a subject I need to return to – in my next post. This post will focus on batteries and storage.

Neoen, a French renewable energy company, is building a 315MW, 99 turbine wind farm near Jamestown in South Australia. Connected to this project will be an array of Tesla’s lithium ion Powerpack batteries. According to this ABC News article:

The array will be capable of an output of 100 megawatts (MW) of power at a time and the huge battery will be able to store 129 megawatt hours (MWh) of energy so, if used at full capacity, it would be able to provide its maximum output for more than an hour.

It will be a modular network, with each Powerpack about the size of a large fridge at 2.1 metres tall, 1.3m long and 0.8m wide. They weigh in at 1,200 kilograms each.

It will have just slightly more storage than the next biggest lithium battery, built by AES this year in southern California.

But Tesla’s 100 MW output would be more than three times larger than the AES battery and five times larger than anything Tesla has built previously.

I’m no electrochemist, but a nice scrutiny of these sentences identifies a clear distinction between output and storage. And the output of this planned battery is the pioneering aspect.

So here’s a very basic summary of how a rechargeable lithium ion battery works. Each battery (and they vary hugely in size) is made up of a number of cells, each a battery in itself. On opposite sides of the cell are conductive surfaces, aka current collectors, one of aluminium and the other of copper. Inside and joined to these surfaces are electrodes, the positive cathode and the negative anode. The cathode is made from a lithium metal oxide such as lithium cobalt oxide or lithium iron phosphate, which needs to have the purest, most uniform composition for maximum performance and longevity. The negative anode is made from graphite, a layered form of carbon. The layered structure allows the lithium ions (Li+) created by the current to be easily stored at and removed from the carbon surface. Between these electrodes, filling the cell, is an electrolyte fluid through which lithium ions flow from one electrode to the other, which charges and discharges the cell. Again the purity of this fluid is a vital factor (research is being done to come up with a form of solid electrolyte). Between the two electrodes is an insulating plastic separator, essential to keep the electrodes separate and prevent short-circuiting. This plastic membrane allows the lithium ions to pass through it. The battery is charged when the lithium ions have passed through the separator and become attached to and stored in the layered graphite of the anode. The battery is discharged by reversing the flow.

Lithium ion batteries are found not only in Tesla Powerpacks but generally in electric car batteries and many other devices such as my own iPhone and iPad. They’re lighter and have much less energy density than lead-acid batteries. The technology of lithium ion batteries is described in a number of useful online videos, of which the most comprehensive, I think, is a webinar from the American Chemistry Society (ACS), essentially an interview with Dee Strand, a lithium ion battery specialist and expert. Her talk also provides interesting ideas on how these types of batteries can be improved.

So a fully-charged cell has stored energy, and a discharging cell is producing output. There are variations in lithium ion battery technology, for example variations in the electrode materials, the electrolyte composition and the like, so we don’t know precisely what Tesla will be using for the South Australian battery system, but we have a fair idea.

In any case, there seems no obvious reason why this proven technology can’t be scaled up to meet the sort of need that was identified after last September’s state blackout. Now we just have to wait and see whether Musk will lose his bet regarding completion time come December.

Refs and info

http://www.tai.org.au/

http://www.abc.net.au/news/2017-07-07/what-is-tesla-big-sa-battery-and-how-will-it-work/8688992

https://www.thermofisher.com/content/dam/tfs/ATG/CMD/cmd-documents/sci-res/pub/comm/env/AR-Lithium-Ion-Battery-Degradation-RandD-Mag-042214.pdf

http://www.abc.net.au/news/2017-07-07/sa-to-get-worlds-biggest-lithium-ion-battery/8687268

Just type in ‘lithium ion battery’ in youtube

 

 

Written by stewart henderson

July 19, 2017 at 1:00 pm