3M has made an investment in Nanoscale Components, a company that has developed a novel, low-cost pre-lithiation process. 3M says its investment will expand the adoption of 3M’s unique silicon alloy anode for lithium-ion batteries. (Earlier post.)
To take advantage of promising high-capacity anode materials such as silicon, sulfur and other lithium-free materials in a next-generation Li-ion battery, either the cathode or the anode needs to be prelithiated—i.e., lithium needs to be inserted into the material. In a 2011 paper in the journal ACS Nano (earlier post) Stanford researchers led by Prof. Yi Cui noted that:
Several prelithiation methods have been reported on Li-free cathode materials, such as hydrothermal treatment with LiCl and chemical reaction with n-butyllithium. However, different applications (grid storage, electric vehicles, and portable electronic devices) may require different cathodes for pairing with Si anodes, for the balance of power, capacity, cost, and safety. Therefore, instead of developing an individual prelithiation method for every Li-free cathode material, it is strategically preferable to develop one single pre-lithiation method for the Si anode and pair it with all the Li-free cathodes.
Experimentally, anode materials are harder to prelithiate than cathode materials because a more reactive Li source is needed; the product is relatively unstable; and the reaction is hard to control. Carbon anodes can be prelithiated using stabilized lithium metal powder (SLMP). In a full battery utilizing such a prelithiated carbon anode and a Li-free V6O13 cathode, a decrease of irreversible capacity was observed in the carbon anode. However, SLMP is expensive and not easily available. A cheaper and simpler prelithiation method is desirable. Moreover, an additional requirement for the prelithiation of a nanostructured Si anode is that the morphology of the nanostructure must survive; otherwise, the huge volume changes during battery cycling could pulverize the Si anode.—Liu et al.
3M says that Nanoscale’s patented process overcomes many of the obstacles of previous pre-lithiation technologies and has demonstrated scalability for battery manufacturers. The company says it has already demonstrated a factor of 50,000 process scalability in initial roll-to-roll manufacturing.
As broadly described in a Nanoscale Components patent application filed in January 2014 and published in October 2014, during the pre-lithiation process, a reducing current is applied to the anode in such a way as to intercalate the lithium. The anode is bathed in a solution comprising a non-aqueous solvent and at least one dissolved lithium salt.
A gas such as CO2 can be sparged into the non-aqueous solution in order to increase salt solubility; increase the ionic conductivity; support the formation of Li2CO3 or Li2SO3 SEI layer; and increase the lithiation efficiency.
Since CO2 is inexpensive, easily dried, chemically safe, and a potential building block gas for a high quality SEI layer, Nanoscale selected it as the preferred dissolved gas. CO2 preferentially reacts with trace H2O and Li+ during the lithiation process to form a stable, insoluble SEI material (Li2O, Li2CO3 etc.). The moisture level in the lithiation tank is driven down by the consumption of CO2 and H2O according to this process, and care is given to control the moisture level in the tank to between about 5 to 20 ppm. In this way, anode lithiation with a quality SEI material is produced continuously.
3M silicon anode materials have more than three times the capacity of conventional anode materials and can increase battery energy by up to 40% when matched with high-energy cathodes.
3M silicon anode materials also have shown excellent cycling and high rate characteristics suitable for a wide variety of applications. The thermal stability of 3M anode Si compositions are comparable to conventional graphite systems. In addition, 3M water-based coating formulations have been designed to fit into conventional graphite coating processes for simplified manufacturing.
The combination of 3M’s silicon alloy and Nanoscale’s pre-lithiation process has proven effective to extend battery life and increase cell energy even further. The companies have demonstrated high performance cells with anodes that hold more than 1200 mAh/g, three times the capacity of state-of-the-art graphite anodes used today.
3M battery materials include anode powder, current collector and electrolyte technologies, as well as cathode IP technology for license. 3M also makes tapes and adhesives for assembly of battery packs and consumer electronics devices.
Nian Liu, Liangbing Hu, Matthew T. McDowell, Ariel Jackson, Yi Cui (2011) “Prelithiated Silicon Nanowires as an Anode for Lithium Ion Batteries.” ACS Nano doi: 10.1021/nn2017167
United States Patent Application 20140310951: “Phased Introduction Of Lithium Into The Pre-Lithiated Anode Of A Lithium Ion Electrochemical Cell”