## UNIST teams develop high-rate iron oxide anode material, high-energy and high-rate cathode material for Li-ion batteries

##### 16 August 2012
 The spindle-like porous α-Fe2O3 prepared from an iron-based metal organic framework (MOF) template showed high capacity and high rate capability. Credit: ACS, Xu et al. Click to enlarge.

Teams at the Interdisciplinary School of Green Energy, Ulsan National Institute of Science and Technology (UNIST) in S. Korea, both led by Dr. Jaephil Cho, separately report on the development of a high-capacity and high-rate anode material for Li-ion batteries in the ACS journal Nano Letters and a high-rate and high-energy Li-ion cathode material in the journal Angewandte Chemie.

For the anode material, the UNIST team prepared spindle-like porous α-Fe2O3 from an iron-based metal organic framework (MOF) template. When tested as anode material for lithium batteries (LBs), this spindle-like porous α-Fe2O3 shows greatly enhanced performance of Li storage. The porous α-Fe2O3 retained 911 mAh g–1 after 50 cycles at a rate of 0.2 C. Even when cycled at 10 C, comparable capacity of 424 mAh g–1 could be achieved.

...graphite, the currently used anode material for commercial LIBs, has already approached its theoretical limit (372 mAh g−1) and seeking alternative anode materials has become an urgent task nowadays. Among those feasible anode materials, α-Fe2O3 has been proven to be a possible candidate because of its high theoretical capacity (1007 mAh g−1), low cost, ease of fabrication, and environmental benignity. The capacity of lithium storage is mainly achieved through the reversible conversion reaction between Li+ and Fe2O3, forming Fe nanocrystals dispersed in Li2O matrix.

Despite of those intriguing features, iron oxide still suffers from poor cyclability that is caused by the drastic volume change during charge−discharge process. The low conductivity of α-Fe2O3 also induces additional performance degradation, especially when charging and discharging at high current densities. To improve rate capability, different α-Fe2O3 nanomaterials with optimized shapes and particle sizes have been fabricated by various methods including thermal heating, controlled hydrolysis, templated synthesis, acidic etching, wrap-bake-peel approach, and so forth. However, there has been limited success in finding relatively simple ways to produce iron oxide electrodes with satisfactory high specific capacity and high rate capability.

...Herein, we report a new method to obtain spindle-like mesoporous α-Fe2O3 with higher surface area by using MOF as template. As fabricated from ordinary materials by a solvothermal process and subsequent calcination, this strategy is simple, inexpensive, tunable, and scalable. More importantly, when applied as anode material, the spindle-like porous α-Fe2O3 exhibits significantly improved electrochemical performance with a high specific capacity of 911 mAh g−1 after 50 cycles at a current rate of 0.2 C. The rate capability is also greatly enhanced, showing 861 and 424 mAh g−1 at 1 and 10 C, respectively.

—Xu et al.

Using a typical iron-based MOF—MIL-88-Fe—as the template, the team utilized a two-step calcination method to prepare the spindle-like mesoporous α-Fe2O3. The resulting material has a relatively high BET surface area of 75 m2 g−1—twice that of mixed Fe2O3 prepared from Prussian blue.

The spindle-like structure consists of clustered porous Fe2O3 nanoparticles with size of <20 nm; pore size appears to be <10 nm. Both the small nanoparticles and pores are critical to the electrochemical performance of this material, the authors noted.

This approach may provide a general way for fabricating porous metal oxides for lithium-ion batteries, the authors suggested.

 Fabrication process and electrical circuit configuration of carbon-coated single-nanoparticle clusters. a) The carbon coating of single-crystal nanoparticles was achieved by sucrose carbonization in air. b) Cross-section and electric-circuit configuration in a nanoparticle cluster. A single-crystal of LiMn2O4 is covered with a thin carbon layer that forms an electrical network in the nanoparticle cluster. Credit: Lee et al. Click to enlarge.

Cathode material. Conventional Li-ion batteries have the drawback of low rate capability, especially during the charging process (that is, the batteries require a long time to charge), Cho and his colleagues note, suggesting that for EVs to become popular, battery charging should be able to be completed in a few minutes—i.e., in a comparable time to that required for filling automobiles with gasoline.

Li-ion rate capability can be improved by reducing the dimensions of the active material; however, the LIBs would then have insufficient electrode density. To overcome this problem, The UNIST team synthesized carbon-coated single-crystal LiMn2O4 nanoparticle clusters as a cathode material; this material can be densely packed on the current collector.

...in the past decade, the synthesis of nanostructured LiMn2O4 having various morphologies has been intensively studied to enhance the rate capability...

The disadvantage of nanosized materials is that they cannot be packed as densely on the current collector as micrometer-sized materials; this fact means that electrodes made of nanosized materials have a high porosity, thus resulting in a decrease the cell capacity. Therefore, the best way to improve both the rate capability and electrode density would be to use micrometer-sized particles that consist of aggregated nanoparticles.

The disadvantage of this arrangement, however, is that the primary particles located around the center of a nanocluster exhibit a large electric resistance because these particles are not connected with the conducting agent, thus resulting in a high overpotential during high-rate charging and discharging. To overcome this disadvantage, we hypothesized that the primary particles in spinel LiMn2O4 nanoclusters could be coated with a thin carbon layer using sucrose as the carbon source. Sucrose carbonization on the single-crystal particle surface resulted in the formation of an electrical network within the secondary particle. The use of this proposed material in a cell afforded not only an extremely high rate capability but also a high energy density.

The resulting carbon-coated single-crystal LiMn2O4 nanoparticle cluster material itself exhibits a gravimetric energy of 300 Wh/kg of active material (kgam) while delivering a power of 45 kW/kgam and a volumetric energy of 440 Wh/liter of electrode (Le) while delivering 68 kW/Le of power. The use of this material would enable the lithium-ion battery to be charged up to 97% in 100 s and deliver more than 63% of the initial capacity after 2,000 cycles without changing power, at the same charge and discharge rates of 20 C (~3 min), according to the study.

The UNIST team evaluated the electrochemical performance of CSC-NPs in pouch-type half cells. First discharge capacity of the CSC-NPs was 120 mAhg-1. Compared with practical capacity at 0.5C, the CSC-NPs retained 95.3% capacity at 10 C (343 s) and 83.1% at 50 C (59 s). These results imply that CSC-NPs can be charged to 95.3% in 6 min and 83.1% in 1 min by the constant current mode, the team said.

The CSC-NPs exhibited discharge capacities of 121 mA h g-1, 108 mA h g-1, and 80 mA h g-1 at rates of 1 C, 50 C, and 100 C, respectively (1 C = 120 mA gg-1). Therefore, a cycle at 100 C takes only 48 s with the cell retaining 66% of its initial capacity.

To investigate cycle retention at high rates, these materials were cycled at a rate of 20C for 2000 cycles. The specific power of a 20 C cycle of an LIB is comparable with that of variable capacitors. With an initial capacity of 110 mA h g-1, 90 % of the initial capacity was maintained even after 400 cycles. Even after 2000 cycles, capacity retention was 63% and more importantly, the specific power did not change for different number of cycles because the average voltage was almost constant with respect to the number of cycles. In addition, a stepwise charging method was used for boosting charge. This charging method can allow the CSC-NP electrode to be charged to 98% of 1 C capacity in 100 s, and 90% of its initial capacity was delivered after 200 cycles.

By using this material, we overcame the low-electrode-density problem of nanosized active materials while maintaining excellent rate capability. The performance is attributed to: 1) fast electro-chemical reaction owing to the nanosize effect; 2) fast ion pathways to reach primary particles, such as grain boundary and particle surface; and 3) high electron conductivity in secondary particles as a result of the carbon coating of the constituent primary nanoparticles.

These efforts are an attempt to connect every single-crystal nanoparticle electrically and ionically in parallel, and we believe that these concepts offer a direct path to improving the rate capability of lithium-ion batteries without decreasing the electrode density.

—Lee et al.

Resources

• Xu, X., Cao, R., Jeong, S. and Cho, J. (2012) Spindle-like Mesoporous α-Fe2O3 Anode Material Prepared from MOF Template for High-Rate Lithium Batteries. Nano Letters doi: 10.1021/nl302618s

• Lee, S., Cho, Y., Song, H.-K., Lee, K. T. and Cho, J. (2012b) Carbon-Coated Single-Crystal LiMn2O4 Nanoparticle Clusters as Cathode Material for High-Energy and High-Power Lithium-Ion Batteries. Angew. Chem. Int. Ed. doi: 10.1002/anie.201203581

### Comments

If this can be mass produced at an affordable cost, it could be one of the first very quick charge battery for extended range BEVs.

This is good news for future extended range BEVs and many more improved versions will come in the next 10-15 years.

This is an industrial catastrophy, they are going nowhere with these batteries and they are waisting billion of dollars worldwide. Stop this waste, the auto industry will collapse and goverments will go bankrupt and petrol compagnies will buy contries for cheap.

Start hydrogen technology right now instead as it apply to everything not just constricted cars that weight like trucks and need impossible long arduous charge time where almost nobody have a private parking along their house. This model of recharging a small bev at home at night is just a pipe dream proposed by big oil to save time concerning hydrogen.

Harvey

What we are seeing now for the EV as commercial product is far from your rosy predictions, even Elon Muck is getting extremely cautious when he sees the dismal sales of the Nissan Leaf.

AD

Hydrogen as a fuel for individual transportation is an hoax, it won't happen. For large trucks we will use natural gas not H2, natural gas is abundant, clean cheap and much more easy to handle than H2 and it can also be made from renewable sources. H2 is such an energy sink to make, store and transport that it will never work.

Hey AD, UNIST is Korean. Are you worried about the Korean budget?

The batteries and EV/PHEVs are directly affecting the oil industry now. Did anyone think that the oil industry wouldn't attack whoever or whatever threatens it's profitability through it's agents on capital hill? Does anyone think we would have fought three wars in the middle east if not for oils influence?

AD is just comic relief; he's not even a decent troll.

The ultra-fast charge and discharge rate of the carbon-coated nano-manganate material makes it ideal for conventional hybrid vehicles.  Operating at 50C, a 1 kWh battery could absorb 50 kW of braking power.  This is way beyond anything currently out there.  It suggests a route forward for something like GM's BAS-II:

• Cut the ICE down to 2 cylinders, like Fiat's TwinAir.
• Use the space freed by the lost cylinders to put a 50 kW induction motor/generator in place of the flywheel.
• Stick the battery in place of the current starting battery.
• Electrify all the engine accessories, allowing full start/stop operation.
Using electronic controls, the motor-generator could easily smooth the torque pulses from the 2-cylinder engine and reduce NVH over much more complex engines.  Add this to the fuel savings and you have a much better car all around.

Well said E-P...it may come around sooner than we think. I stll maintain that by 2020 or shortly thereafter, we will have improved affordable HEVs with 70+ mpg at the same price as ICEVs; improved more affordable PHEVs with 100+ mpg and much improved BEVs with 120+ mpge. Better much lower cost batteries will be around.

At about the same time, many heavy vehicles such as highway buses, large trucks, locomotive, ships, heavy machinery etc may be using FCs.

EV won't do better than HEVs in term of sales so in 2020 they will do 2% of sales just as HEVs today 10 years after their introduction. And talking about sales of HEVs without Toyota the sales of HEV would be strictly "0". So the number could be enven worse if EV don't find a Toyota successful promoter...

large trucks won't use FCs their power density is too low and their cost too high

Tree...please do not use USA as the sole guide post. Electrified vehicles already have close to 50% of sales in Japan and are gaining in many other countries. Our local HE-MEN/Cowboy reputation with our Hummers and our acquired conviction that large gas guzzlers mean richness is not common everywhere. Even in USA, about 30% are now prepared to consider to buy smaller electrified vehicles. USA may be the last country to go electric and use the Metric system but Americans will eventually find out that resistance is futile.

Yes but Japan is always an exception in almost everything so I am not sure that their example is necessarily a good predictor for other countries. In Europe sales of HEV are even worse than in US, almost nil, why ? because they have small diesel that top 3.5L/100Kms 70MPG try to beat that even with an EV. an EV can get 100MPGe but the extra-price upfront is dissuasive. So 2 % of EV in 2020 is still pretty good that's 1.5 millions car a year but it won't make a dent in our oil addiction. PHEV look more promising at this point but the complexity of this approach is problem to reduce the cost.

Tree...you seem to forget that new technologies always cost more for the first 10-15 years. So did HDTVs, Digicams, PCs, Printers, small lithium batteries, etc. Diesels are over 120 years old and modern electrified vehicles are just coming to the market place. It takes a few decades for one technology to replace another, specially with loads of  from the oil and farming (ethanol) industries.

Yes, EU has found a compromise with more efficient (dirty) diesels but they will electrify their vehicles just as they have electrified their trains. EU does not produce a very high percentage of the diesel oil used for their vehicles and it would make sense to switch to other sources of cleaner energy. It will come.

USA may be one the hardest nation to change because Americans still (wrongly) think that they are the best and can do no wrong. The current mismanagement and resulting long lasting economic recession and the accelerated transfer of wealth from the 97% to the 3% may foster different thinking soon.

Harvey

if you could buy 15K electric vehicle that can drive 250 miles without recharge then I would say you are right. But we are not there yet unfortunately...in the very best case the battery technology for a 250 miles vehicle won't be here before 7 years then the cost has to go down and it takes time.

You don't need an EV that can go 250 miles without a recharge; an EV that can go 100 miles and swap in a new battery pack in 3 minutes will do.

''an EV that can go 100 miles and swap in a new battery pack in 3 minutes will do.''

LOL Battery swapping.

Tree...already the new 2013 Leaf will do 25% better than the current model and will be much cheaper. If 25% can be done every 2 to 3 years and cost simultaneously reduced, the 250 miles, \$15K (very basic) EV made in India or China may very be around in about 7 years. It is a bit too soon to place an order, but one can start planning for it.

I do not strongly believe that battery switching is a long term viable solution. Future very quick charge improved batteries will not have to be switched for at least 10+ years. A quick charge every 500 Km will be enough. The extra weight of 100+ Kwh batteries can be partly compensated with lighter vehicle bodies and accessories, at least until such times as batteries performance is increased from under 200 Wh/Kg to over 600 Wh/Kg. Post 2020 batteries will meet those requirements. Post 2025 batteries will do even better.

Battery switching may not be necessary in 2030, but it works with today's cells.  There's also the little detail that a pack-swapping system allows smaller and cheaper batteries to be used regardless, the vehicle to have greater uptime (useful for e.g. taxi service), and even completely different cells to be swapped in (for instance, switching to a zinc-air pack for a long highway leg).

The American landscape is littered with the shells of former pay telephones.  Would it be a bad thing if the landscape of 2040 has the foundations of former battery-swap stations?  I don't think so; the faster we get started on electrifying transport, the better.

New technologies and more efficient manufacturing, such as very long low cost Roll to Roll graphene sheets from Sony-Japan, etc., will yield superior lower cost batteries by 2020 or so. About at the same time, additive layer (3D printing) will make possible much lower cost, lower weight, composites car body parts. The outer layer of all exposed portions of the vehicle (roof, booth, hood, windows etc) may convert sunlight to usable electricity to extend e-range and/or recharge the batteries while parked.

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