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Mitsui Mining and Smelting Develops New Silicon-Based Anode for Li-Ion Batteries

Silx
Cross-sectional views and structure of SILX. Click to enlarge.

Mitsui Mining & Smelting Co., Ltd. has developed a new silicon-based anode material—SILX—which enables higher capacity and power in rechargeable lithium-ion batteries. The company plans to begin commercialization of SILX in 2010 through partnerships with battery manufacturers and OEMs.

Silicon is conceptually an attractive anode material for lithium-ion batteries because of its high theoretical charge capacity (4,200 mAh g-1—more than 10 times that of graphite anodes and much larger than various nitride and oxide materials) and low discharge potential. However, silicon anodes are problematic because the material’s volume changes by up to 400% upon the insertion and extraction of lithium ions during charge/discharge cycles. This results in pulverization and capacity fading.

Mitsui Mining & Smelting addressed this by covering the silicon with thin copper and creating a structure with spaces to accommodate the swelling of the cell inside its negative electrode.

The capacity density of a SILX anode is approximately twice that of conventional carbon-based anodes, according to Mitsui. The energy density of the resulting li-ion battery will be 30-50% higher than current products. A battery using SILX anode material will store more energy (higher capacity) and generate more power (higher output).

The company is now investigating a suitable cathode partner for SILX anodes, as well as establishing the technology for mass production to accelerate commercialization through partnerships with battery manufacturers and OEMs.

The development of SILX was undertaken by a project team under the direct control of the Chief Technology Officer of Mitsui Mining & Smelting. The team leveraged technologies from other business units of Mitsui Mining & Smelting such as battery materials, powdering, electrochemistry, and copper foil.

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Comments

Dr. John De Roche

This anode concept has been around for a while. As indicated in the report; the volume changes during charge/discharge cycles have proven a serious drawback to commercialisation. I am rather sceptical that such cells based on a copper support would have a large cycle life, and long service life. There are two possible scenarios of realistic application:

1) Usage of a very narrow capacity window to reduce volume change stress on the molecular matrix. In this constricted scenario, I can assume from current information that the speculated 30 to 50 % higher energy density would cancel out any advantage over current conventional cell. Who utilise large capacity windows.

2) Application of some form of highly porous secondary scaffold like material to fulfil the function support matrix, while the silicon anode material is left to intercalate with the lithium ions.

It remains to be seen.

Rafael Seidl

@Dr. John de la Roche -

I think your approach #2 should prove more fruitful. Use a highly porous and electrically conducting matrix material and cover it with silicon nanoparticles that act as lithium ion sponges. The hard part will be maintaining electrical contact between the matrix and the nanoparticles, which must also not coalesce. I'm not sure how this could be achieved, though.

Firefly Energy uses a carbon foam matrix with relatively coarse pores to increase the surface area of a lead coating. Simply replacing that coating with silicon probably wouldn't work because the very high change in volume would induce high compressive stresses in the coating surface.

Neil

Re: solution #2. isn't that roughly what they've done with the copper coating that by reserving the space effectively creates a conducting secondary scaffold?

Larry

Question? Does the development of improved anode materials alone allow the greater battery capacities and charge rates or do equivalent improvements in cathode chemistries and designs also need to occur? I'm not as up on my battery chemistry as I should be but I note this is about the third or fourth article on improved anode methodologies I've seen here on GCC in the past week or so, but I can't recall any on cathode improvements. Is current cathode development satisfactory? Are their such improvements in progress?

Northernpiker

Larry,

A battery has three main components, cathode, anode and electrolyte, and five main attributes – energy storage, power capability, life, safety and cost. If only one attribute was meaningful, then the designer would give each component the same capability; otherwise, one or two of the other component has wasteful, excess capability. However, a battery design represents a trade-off of energy, power, life, safety and cost and, as a result of this compromise, battery components would have different capabilities to support the individual attributes of the battery.

So, a new cathode material with double the original cathode’s energy storage capability would not double the battery’s energy storage capability unless the existing anode and electrolyte could support a doubling of the energy storage. However, you could halve the physical size of the cathode. If the cathode represents 1/3 the size of the battery, then one could reduce size of the battery by 16.7 % and obtain the same energy storage capability, i.e., increase energy storage per unit size by 20%, so long as the new cathode has power, life, safety and cost attributes equal to or better than the original cathode. The same mathematics would apply to an anode, e.g., Stanford’s nanowire anode announced in December, 2007 that is claimed to offer a 10 X improvement in performance.

As for recent developments in Li-ion cathodes, here is an excerpt from an article on a Argonne National Labs development. Notice it claims about a 25% improvement in the battery based on a 50% improvement in the cathode.

“The electrode material can store 45 percent to 50 percent more energy than the best electrodes in laptop batteries. In terms of an entire battery cell--given that the positive electrode represents less than half of the total weight and volume of a battery cell--the total energy storage of the battery can be improved by 20 percent to 30 percent”

http://www.technologyreview.com/advertisement.aspx?ad=energy&id=30&redirect=%2FEnergy%2F20524%2Fpage1%2F%3Fa%3Df

The article goes on to note that the new cathode material does not support a high power rate but it is more stable than the cathode material used in laptop and cellphone batteries.

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