## Three groups under DOE BATT program independently synthesize silicon-based high-capacity anode materials for Li-ion automotive batteries

##### 17 April 2012

Three groups funded under the US Department of Energy (DOE)’s Batteries for Advanced Transportation Technologies (BATT) program (earlier post) have independently synthesized silicon-composite nanostructures as Li-ion anode materials with excellent capacity retention with greater than 800 mAh/g reversible capacity. Silicon is of great interest as a high-capacity anode material, but has been hampered for commercial automotive applications because of its short lifecycle and capacity degradation. (Earlier post.)

Prashant N. Kumta, University of Pittsburgh; Ji-Guang Zhang and Jun Liu at Pacific Northwest National Laboratory; and Yi Cui at Stanford University are pursuing different approaches to developing alternative silicon-based anode materials to replace graphite to provide higher gravimetric and volumetric energy density in Li-ion batteries. Their progress is outlined in the First Quarter FY 2012 Report for the BATT program.

Kumta. Kumta is searching for inexpensive silicon, carbon, and other inactive matrix based composite powders that provide 1) an electrochemical potential a few hundred mV above the potential of Li, and 2) a capacity of 1200 mAh/g or greater (>2600 mAh/ml). The research is focused on exploring novel economical methods to generate nanoscale heterostructures of various Si nanostructures and different forms of C derived from graphitic carbon, nanotubes (CNT) and new binders.

His team has synthesized nano-scale electrodes comprising Si-graphitic carbon-polymer derived C, and carbon nanotube (CNT) related systems; the nano-composite Li-Si-C hetero-structures exhibit stable capacities of 700-3000 mAh/g.

By the end of the third quarter 2012, Kumta expects to have generated nano-composite core-shell, random, and aligned structures of varying nanoscale Si morphologies, boron (B), and C nanotubes exhibiting 1500 mAh/g and higher capacities. The group is working to generate novel binders, study the synthesis conditions, nano-scale microstructure affecting the energy density, rate capability, first cycle irreversible loss and coulombic efficiency, characterize the SEI layer, and outline steps to yield stable capacity, reduce irreversible loss and increase coulombic efficiency.

Zhang and Liu. The approach of Zhang and Liu is to manipulate the nano-structure and conductivity of silicon (Si)-based anodes to improve their mechanical and electrical stability.

One approach has been to investigate porous silicon with micrometer particle sizes and different nanopore sizes.The porous Si powders have been coated with a thin layer (~6% in weight) of carbon by chemical vapor deposition (CVD) to increase their electrical conductivities. The porous structure of Si helps to accommodate the large volume variations that occur during Li-insertion/extraction processes.

So far, they have obtained an initial capacity of ~1200 mAh/g (based on the full electrode) and capacity retention of ~800 mAh/g over 30 cycles at a 0.1C rate with that material.

In another effort, they developed a SiC/SiO/C core-shell composite, which showed an initial capacity of ~1000 mAh/g (based on the full electrode) and capacity retention of ~600 mAh/g over 100 cycles.

By the end of Q3 2012, they expect to have prepared micro-sized Si particles with large nano-pores will be prepared, with a targeted initial capacity of >1000 mAh/g (based on electrode) and capacity retention of ~700 mAh/g over 100 cycles will be obtained. They will investigate a SiC/Si/C (or SiC/SiO/C) core-shell composite further to improve its performance with a targeted initial capacity of >1200 mAh/g (based on the full electrode) and capacity retention of ~700 mAh/g over 100 cycles.

Cui. Cui and his team at Stanford are exploring new types of Si nanostructures, specifically, a variety of hollow and porous nanostructures. They have fabricated a variety of spherical, one-dimensional, tubular, and porous Si nanostructures into Si anode architectures.

Enclosing Si nanoparticles in a thin tubular carbon shell within which there is space for unimpeded volume expansion during lithiation allowed for the outer carbon layer to remain intact even after full lithiation and expansion of the Si nanoparticles. This composite material showed excellent cycling behavior in Li half-cells, retaining >85% of the initial discharge capacity after 200 cycles with CE >99% after the initial 50 cycles.

By the end of Q3, Cui expects to have optimized anode cycle life, Coulombic efficiency, first cycle irreversible capacity loss, specific capacity, and mass loading by varying synthesis conditions.

Resources

More and more possibilities coming out for future improved batteries. Could the 100+ research groups get their act together and build an improved battery by 2017 or so?

Maybe the start of a real convergence and some real product at the end. But never claim victory too soon, a new material is often deceptive, big promise can end up in a failure simply because of stupid problem of manufacturing despite great performances. But the diversity of approaches here might yield at least one robust solution.

We see lots of battery stories on GCC, but I believe battery chemistry is on a roll, enough resources have been focused on making progress and they are. Just give people a $10+ billion dollar annual market and they pay attention right away. I think you'll see something in the next year, or already have. The problem is that while many peope have made cells that are higher energy, it takes years to evaluate the safety aspects, reliability, cycleability etc., and on top of that when things are near commercial the companies want to be a little tight lipped about the specifics. This makes it difficult to assess the reasonability of the claims. A good example is the recent press release by Envia. They may really have something but the specific information in the release was not adequate to make a judgement, nor would you expect it to be. Unfortunately many companies are capable of living off the press release like hype statements, which spin positive with insufficient technical content. Investors perform due diligence and rightfully so. We are just observers in the gallery complaining that no one gives us any information. It was a lack of a$10B market that stymied the CARB EV initiative two decades ago.  What was really needed given the battery tech of the day was a PHEV mandate, not a ZEV mandate; that would have moved enough units to generate the sales volumes to get R&D moving.

We lost 20 years.  It looks like we're not going to lose any more, and I'm very glad.

also dont forget the H2 diversion, it stole a lot of steam from progress.

E-P...wonder what would happen (again) if crude price drop as it did in the late 1970's and 1990's. Changes are that it will not and HEVs, PHEVs and BEVs will continue to be developed. Meanwhile, batteries are steadily improving and so are most associated electric and electronic components. Special lighter weight bodies will also be around soon to further improve EV's performance and lower cost.

The excess oil production capacity that existed through the late 90's has vanished, eaten by depletion.  If crude price drops again, it'll be because of another major economic contraction.  People won't have the money to buy fuel even if it's cheap.

One hopes they'll learn their lesson and keep their fuel needs as low as possible, but when the political narrative ignores the fact of peak oil it's very hard to get this through people's skulls, let alone act on it.

We are still a battery chemistry or two away from a fully competitive automotive battery technology. Improving around the edges will prove to be no more successful that improving the Pb-acid approach was.

I don't know whether Li-Air chemistry will do it, but Li-Ion has arrived and replaced NiMH, but it isn't enough.

Its closer to the target, but its still no cigar.

Meanwhile the ICE technologies are making huge strides now. Efficiencies are rising, and cleanliness equivalent to (and even better!) then the EV have arrived, for the Otto cycle, if not for the Diesel cycle, as yet. (Clean ICEs cleanse the Air while EVs don't.)

So there is a moving target to match or exceed, while concerns over fossil reserves has largely abated.

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