Earlier work at ANL on novel silane compounds for use as non-aqueous electrolyte solvents in lithium-ion batteries found that the silane molecules can easily dissolve most lithium salts including LiBOB, LiPF₆, LiBF₄, and lithium trifluoromethylsulfonimide.

Among the findings of that study, reported in the journal Electrochemistry Communications, were:

• LiBOB salt was found to be very appropriate for these silane molecules because, unlike LiPF₆, LiBOB can provide a good passivation film on a graphite anode.
• Cyclic voltammetry analyses show that silane-based electrolytes with a 0.8 M LiBOB salt concentration are stable to 4.4 V; they also exhibit very high lithium-ion conductivities up to 1.29 x 10^-3 S/cm at room temperature.
• Full cell performance tests with LiNi_0.08Co_0.15Al_0.05O₂ as the positive electrode and MCMB graphite as the negative electrode showed excellent cyclability both at room temperature and at 40 °C.
• Cells with these new silane electrolytes exhibit long calendar life; they show no impedance rise after aging at 80% state of charge and 55 °C for one year.

The results, the Argonne researchers concluded, suggested that silane-based electrolytes have great potential for use in lithium-ion batteries.

EnerDel is currently wrapping up an 18-month, $2.5 million USABC research project, 50% cost-shared with DOE, in partnership with ANL on developing a battery system that matches the safety of its lithium titanate anode (Li₄Ti₅O₁₂) with a safe, high voltage 4.8V spinel cathode (LiMn_1.5Ni_0.5O₄ as the main candidate) to support a 10-mile electric range plug-in hybrid electric vehicle (PHEV 10) application.

As reported at the DOE Merit Review in May, by Cyrus Ashtiani, EnerDel has achieved 130 mAh/g (versus a theoretical 147) and 630 mWh/g with LiMn_1.5Ni_0.5O₂ material. One of the technical challenges in that project, he said, is the development of a high voltage electrolyte.

EnerDel and Argonne earlier cooperated on the development of the lithium titanate battery chemistry, for which they shared the R&D 100 Award for excellence in technology and innovative design from R&D Magazine, and an Excellence in Technology Transfer award.

We are pleased to pursue another breakthrough technology working with the leading national lab in the US for transportation and one of the world’s most technologically innovative car companies. This is an opportunity to make a major new contribution to the future of electric drive in the US and to forge a closer relationship with a major global car maker.

—EnerDel Chief Operating Officer Naoki Ota

Separately, Argonne has also launched a 100% DOE-funded project in partnership with the University of Rhode Island and CSIRO in Australia on novel electrolytes and electrolyte additives for PHEV applications.

Performance, calendar-life, and safety characteristics of Li-ion cells are dictated by the nature and stability of the electrolyte and the electrode-electrolyte interfaces.

—Daniel Abraham Argonne National Laboratory, DOE Merit Review, May 2009

Ideal characteristics for an electrolyte would include:

• Wide electrochemical stability window, 0 to >5 V
• Wide temperature stability range, -30 to +50 °C
• Non-reactivity with other cell components
• Excellent ionic conductivity to enable rapid ion transport
• Negligible electronic conductivity to minimize self-discharge
• Stability for more than 5,000 deep-discharge cycles
• Stability over the 10-year battery life

This project at Argonne is proposing three approaches:

• Investigate novel electrolytes that include glycerol carbonate, and modifications thereof. The modified glycerol carbonates will include methyl ethers, ethyl ethers, and oligoethylene oxide ethers.

• Investigate electrolyte additives designed to react and stabilize the cathode surface to improve cell calendar life. The additives include unsaturated ethers, polyunsaturated alanes, and vinyl silanes.

• Examine room-temperature ionic-liquids (RTIL), and mixtures of RTIL and organic electrolytes, to enable high-safety, high-performance batteries.

Initial studies have focused on developing techniques to prepare high-purity glycerol carbonate, and the electrochemical data obtained with these GC-based electrolytes appear promising, Abraham said in May. Experiments with electrolyte additives designed to protect the positive electrode also show promise.

Resources

• Khalil Amine, Qingzheng Wang, Donald R. Vissers, Zhengcheng Zhang, Nicholas A.A. Rossi, Robert West (2006) Novel silane compounds as electrolyte solvents for Li-ion batteries. Electrochemistry Communications, Volume 8, Issue 3, Pages 429-433 doi: 10.1016/j.elecom.2005.12.017