The Bestest Battery?

Updated: Feb 28



Lithium ion batteries (LIBs) are all the rage. However there are many variations of LIBs available to consumers, with different cathode materials and different anode materials. So how do we know what to buy? Which type is best for what? GEOFF EDWARDS has the answers...


It seems LIBs are everywhere. In our phones, our computers, and increasingly in our cars and homes. In home energy storage systems in particular the customer has a plethora of products to choose from. There is a large range of LIBs, with different cathode chemistries and some with different anode chemistries. So let’s dive into more detail and learn more about what fits where.


CATHODE MATERIALS

Common cathode materials include lithium nickel manganese cobalt (NMC), lithium nickel cobalt aluminium (NCA) lithium cobalt oxide (LCO), and lithium iron phosphate (LFP) (there are other cathode materials that are used only at small scale which we won’t consider).


LCO is an easy one. Its high voltage and high energy density make it perfect for portable applications where space and voltage are important. Mobile phones and tablets are examples. LCO is not utilised for electric vehicles and energy storage, primarily due to cost (high in cobalt) and lifetime (phone batteries are designed to last 500-1000 charge/discharge cycles, whereas electric vehicles require several thousand cycles and energy storage systems more than that). Pretty much all market projections have battery demand in electric vehicles then in energy storage systems swamping mobile applications. Therefore demand for minerals is not expected to be driven by LCO.


LFP was the major cathode material in LIBs for a long time. Recent Nobel Laureate John Goodenough was ‘good enough’ to develop LFP materials and related patents that have earned royalties for 20 years. However, consumer demand for higher energy densities, particularly in electric vehicles, has seen NMC taking over market share from LFP, particularly in the west. China still has some users of LFP in electric vehicles. BYD is probably the largest user with both cars and electric buses. While NMC is dominating electric vehicles, LFP may still have a major role to play in markets where space is not so critical. In energy storage systems, potentially lower cost and longer lifetime for LFP can outweigh disadvantages of lower energy density.



‘Nickel content relative to total metal content in NMC has increased from about 30% to over 80%’

NMC has certainly become the dominant cathode material driven primarily by higher energy density. One aspect of these materials that battery companies love is that they are capable of continual improvement.


Reducing cobalt and increasing nickel have twin benefits of reducing cost and increasing energy density, with the disadvantage of worse stability. This disadvantage has been overcome in recent years and nickel content relative to total metal content in NMC has increased from about 30% to over 80%. Johnson Matthey Battery Materials has recently announced its own version of NMC, called elNO (enhanced lithium nickel oxide) that it claims beats every other version of NMC in key metrics.


NCA has the highest energy density of all cathode materials (see Figure 1) although NMC is catching up. High energy density is why Tesla chose NCA as its preferred cathode material. The difficulty with NCA is stability. If you took the batteries out of a Tesla car and cycled them between charge and discharge in a normal way, you would be lucky to get 500 cycles before the batteries needed to be replaced. Hardly enough for a driver who has just forked out a couple of hundred grand for their shiny new Tesla.


The answer to the low stability comes through battery management. A lot of Tesla’s IP is tied up in knowing how the batteries end up actually being used in cars and how to manage them. Notably, nearly all other electric vehicle manufacturers have gone with NMC.


It will be interesting to see, given the increased energy densities being achieved with NMC, whether Tesla sticks with NCA over NMC, or whether it decides that the energy density advantage no longer outweighs the more complicated battery management required for NCA.


Either way, demand for nickel and cobalt will no doubt continue to rise in the coming years, driven primarily by electric vehicles.


Figure 1. Energy densities (Wh/kg) for cells made from different types of batteries.


The market of most interest in LFP vs NMC is energy storage systems where the extra energy density of NMC is less of an advantage. LFP should have advantages with cycle life and cost, although excellent cycle life also requires excellent anode technology to get the best out of the cathode material.


A summary of home energy storage systems available in Australia is given in this website https://www.solarquotes.com.au/battery-storage/comparison-table/.


Of the systems that disclose the cathode chemistry, 15 use NMC and 22 use LFP, however NMC users include major suppliers Tesla and LGChem. Nearly all the systems have the same warranty (10 years). Development of longer life and longer warranty cells is critical to both reducing the cost of energy storage and promoting potential benefits of LFP over NMC. It’s not much use to the customer if the longer life of the cells isn’t reflected in the warranty.


As mentioned previously, long life cells require the battery company to have excellent anode technology, in addition to good cathode materials. This is well demonstrated by comparing the cycle stability of Sony LFP cells. Good Chinese manufacturers of LFP cells would consider a cycle stability of 6000 cycles at 80% depth of discharge (DOD) as being very good. (DOD is how much of the cells energy is actually used: you can always extend battery life by not charging and/or discharging fully). Sony, however, boast 8000 cycles at 100% DOD, so in addition to longer life, you are able to use the whole capacity of the battery. These considerations are vital in calculating the economics of energy storage (more about this later).


As highlighted in a previous post, safety is a key issue in lithium ion batteries. There has been a fair amount of marketing material spread around in Australia talking about LFP as the ‘safe’ battery. While this has some basis in fact (LFP has inherently less thermal runway than most nickel-based materials) safety is dependent on many factors, not just cathode chemistry.


Panasonic told me about 8 years ago that they had successfully managed stability and safety issues with NMC and were selling off their LFP assets. Their success is demonstrated in the excellent track record of the Tesla PowerWall. NCA could be considered a ‘dangerous chemistry’ however, Tesla has successfully managed lifetime and performance of NCA cells in their electric vehicles.


Safety comes down to proper cell manufacture and proper battery management. If these are done diligently then safety risk is low. If these are done poorly, well, a poorly made and/or managed LFP battery can still blow up.


ANODE MATERIALS

By far the most common anode material is graphite. Graphite can produced two ways: synthetically, and by mining and processing natural graphite. Synthetic graphite has historically been more expensive however, costs are coming down. Natural graphite costs are also coming down, in part due to the plethora of junior graphite companies that have found good graphite deposits. The fight between synthetic and natural graphite is certainly a major issue for multiple Australian-owned natural graphite companies.


Increasingly, the dominant factor in graphite will become lifetime. At the anode in lithium ion batteries, the electrolyte reacts with the surface of the anode material. For good anode materials, a stable coating forms and stops or drastically slows down this reaction, consequently producing a good cycle life. In poorer anode materials the reaction continues (at a slower rate), consuming lithium ions and building up a barrier at the anode surface. This leads to poor cycle life.



Next Generation Rechargable Battery

Development of highly stable anode materials is therefore a key part of lithium ion battery technology. This is married with electrolyte development: high quality electrolytes can passivate surfaces and stop surface reactions. Whether natural or synthetic graphite wins out will depend on how their relative cycle lives compare to their relative costs.


For the consumer, the anode composition will be a mystery as it is never disclosed. Many cell makers, including Tesla, utilise a combination of natural and synthetic graphite. So the battle between natural and synthetic graphite will fly beneath the radar of consumers, but it certainly won’t be beneath the radar of natural graphite companies such as Syrah Resources.


Novonix is an interesting Australian-owned company focussed on producing high quality graphite (it also has an excellent natural graphite deposit in Queensland). An important part of this company’s IP lies in testing. When targeting cycle lives in excess of 10,000 cycles, it is vital to have a reliable accelerated test, otherwise the testing can take years! Novonix (and others) has IP in both testing and equipment to enable reliable prediction of long term life using short term testing.


This is an essential piece in developing high quality, long life anode materials. Interestingly Novonix has pushed towards developing synthetic graphite production in USA, despite having an excellent natural graphite deposit.


Considering the economics section below, it seems highly likely that lifetime performance will dominate over cost for graphite anode materials. Synthetic graphite may well win out on performance however, improvement of natural graphite products will also no doubt continue.


Silicon is another anode material that is considered “next generation”. Silicon has more than ten times the energy density of graphite, but has numerous problems, especially limited cycle life due to expansion and contraction with lithium ion insertion and release. The amount of silicon in batteries has slowly been increasing: apparently Tesla uses a few percent silicon in their anodes. Companies such as Sila Nanotechnologies have raised a lot of money to address this problem. It remains to be seen whether they can hit the stringent price targets to be commercially viable at large scale.


The other interesting anode material is lithium titanate, or LTO. LTO is very different to graphite in that it operates at a much higher voltage. This has the advantage that no reactions occur with the electrolyte. One of the outcomes of this is that lithium dendrites, which cause the majority of safety incidents in lithium ion batteries, do not form. Hence LTO cells can have ridiculous cycle lives (20,000 to 40,000 and even more) and can be charged and discharged extremely quickly.


'With the better systems, expected lifetimes are 15 years rather than the warrantied 10 years which make the economics work'

Until recently, the largest battery deployments in the world were LTO cells used for frequency modulation. Unfortunately, the disadvantage of having the anode at a higher voltage is that the voltage of the cell is much reduced and this leads to much lower energy density and hence, increased cost per kWh.


An Australian company, Zenaji, is offering its Aeon LTO cells for home energy use, with a 20 year warranty. Even though its initial cost is higher (at least 1.5 times other offerings), a 20 year warranty compared to a 10 year warranty may make this a better option for some. A word of warning though: a proper economic analysis should include a capital cost which can change things quite a bit (a lot of data you see on the internet does not factor in a capital cost).


ECONOMICS

Obviously economics (together with safety) are a major driver for energy storage.

The benchmark figure that is commonly used for storage (and energy) is called “levelised cost of storage”, or LCOS. It’s basically the price you would need to sell electricity at to break even, or, put another way, what you would have to be currently paying for electricity to break even on the investment. It includes a cost of capital (i.e. if you invested the money elsewhere you would get a return on the investment). I used 5% for homeowners and 8% for larger installations. The numbers also include cost estimates for inverters. They were calculated using the excellent tool at https://energystorage.shinyapps.io/LCOSApp/.



Figure 2

A few things stand out. Firstly, homeowners are paying extremely high prices for their systems. Given that the cells used are exactly the same as those used for large scale energy storage systems, it’s not immediately obvious why this should be the case. Maybe marketing costs are high, maybe there’s too many fingers in the pie (too many markups) or maybe companies are grabbing high profit margins while they can. And, as I think everyone is aware, on an economics basis alone home energy storage doesn’t make sense.


Hopefully, at least with the better systems, the expected lifetimes are 15 years rather than the warrantied 10 years which would make things considerably better.

For industrial applications, the situation is different since many companies have to pay significant ‘demand charges’ based on maximum power usage. If these are high, or you are in South Australia paying $0.43 per kWh, then batteries can work. Otherwise they don’t.


Numbers for the National Renewable Energy Laboratory (NREL) 2019 benchmarks for large scale energy storage are also shown. It’s hard to know where the latest prices from the large cell making companies are currently at compared to these numbers, since they don’t make prices publicly available. NREL have good connections so we can assume they’re not far out. At 15 years warranty, the costs approach something sensible. Moving to 15 years, 1.5 cycles per day improves the economics a lot. This shows the importance of setting up systems that cycle more than once per day.


To really change things, numbers for a theoretical company called “NewCo” are shown in Figure 2. NewCo is able to source packs for ESS at similar price to current prices for EV packs (see Figure 3 below: up-to-date figures are about $USD156 per kWh average). $0.12c per kWh LCOS for storage is getting to the point where big changes can happen.


Figure 3.


When combined with the latest wind/PV plants, this could deliver continuous energy at about $10c per kWh. South Australia would kill for this.

Coming back to the cathode materials, if LFP is to dominate energy storage over NMC then it must be backed up by warranties that are longer and with more cycles, leading to real cost reductions. This is key to expanding the application of lithium ion batteries in large energy storage systems and could pave the way for a resurgence in LFP batteries.


RECYCLING

With the numbers of lithium ion batteries metastasizing, the issue of recycling is gaining more and more importance. This will only continue as the current generation of EVs age and the batteries reach their end of life.


Recycling is also topical in Australia, with both Lithium Australia and Neometals both recently announcing international deals with their respective recycling technologies.


Most recycling work to date has focussed on the more valuable cobalt, and to a less extent nickel and other metals. One large Chinese cell maker told me that part of the push towards NMC from LFP was because of better recyclability. This balance may change a bit if someone can successfully reclaim lithium during recycling. As one company CEO remarked, the lithium metal content in a battery is orders of magnitude higher than in lithium ores. And as pointed out in the “In the Mix” article in the last edition of this magazine, the cost of lithium in typical NMC batteries is more than the cost of cobalt! In LFP batteries lithium is by far the major mineral cost.


It will be interesting to see if anyone can crack reclamation of lithium using recycling.

SUMMING UP

Its highly likely that NMC-based LIBs will continue to dominate the rapidly expanding EV market where its high energy density gives it a distinct advantage over LFP. It will be interesting to see whether Tesla moves to NMC from its current NCA LIBs.


In energy storage systems the situation is less clear. LFP can compete since energy density is less important, and it has potential to deliver cycle life and therefore cost benefits. Longer life needs to be reflected in longer warranties to significantly change economics. Nevertheless, NMC development and improvement continues apace so definitely worth keeping tabs on this battle.


High quality anode materials also have a key role to play in increasing lifetime and decreasing cost. This could have major consequences for the battle of synthetic graphite vs natural graphite. Natural graphite players should certainly be investing in improved downstream anode products: many of them are.

© 2020 by New-Energy Partnership

Publishers of New-Energy Resources Magazine

  • Twitter Clean