AABC 2014 LLIBTA Symposium - Large Lithium Ion Battery Technology and Application - Track A: Cell Materials and Chemistry - Session 2

Interphases support Li ion intercalation and protect the electrolytes from decomposing at extreme potentials and temperatures. However, their chemical nature, formation process and morphology remain little understood due to their sensitive nature and the lack of reliable characterization means.

In this work, we attempted to develop an in-situ quantitative methodology to monitor the live-formation of interphases on electrode surfaces during the first charging cycle of Li ion battery. The combined approaches reveal how the electrolyte additives change the chemistry and hierarchical structure of the formed interphases.

Fluorinated organic solvents have long been investigated for many applications in lithium-ion batteries. Compared with the SOA electrolytes, fluorinated solvents bring a variety of benefits to the electrolyte. For example, fluorinated cyclic carbonate has been used as a co-solvent or as a solid electrolyte interface (SEI) formation additive for graphite and silicon anodes. Fluorinated carbonates and fluorinated ethers are reported as non-flammable electrolytes non-aqueous lithium ion batteries. However, there is little study about the performance of these fluorinated solvents in the high voltage Li-ion battery.

Since fluorinated molecules have higher oxidation potentials than their non-fluorinated counterparts due to the strong electron-withdrawing effect of the fluorine atom, fluorinated solvents are good candidates for high voltage electrolyte application. In this talk, we will present our recent results on the fluorinated electrolytes which can significantly improve the performance of the high voltage Li-ion cell based on LiNi_0.5Mn_1.5O₄/graphite couple, especially at high temperature.

Due to recent events involving fires, there has been increased scrutiny on the safety of lithium ion batteries used in transportation and stationary applications. A key component contributing to the safety of the lithium ion battery is the electrolyte. Current electrolyte solvents are voltage sensitive and flammable. In addition, the chemical interaction between the electrolyte and the active components in the battery is critical to the safe operation of the battery. The stability of electrolyte will become increasingly important as battery systems in automobiles migrate to higher voltage. Fluorochemicals provide an interesting alternative for lithium ion battery designers due to their high thermal and electrochemical stability as well as their low flammability. This innate stability is due to the strong covalent bonds between carbon and fluorine.

This presentation will examine safety and high voltage improvements by:

• Calorimetry of electrolytes with charged electrodes
• Abuse test results
• High voltage characteristics of the fluorinated electrolytes compared to conventional hydrocarbon electrolytes

The investigation of surface reactions of electrolytes with the electrodes of Lithium Ion Batteries (LIB) for Electric Vehicle (EV) applications will be presented. The beginning portion of the presentation will focus on three novel techniques which have been enabled by the use of Binder Free graphite anodes. This unique combination of techniques has allow us to develop significant new insight into the anode SEI formation mechanisms and structure.

• A novel method which allows straightforward analysis of the anode Solid Electrolyte Interphase (SEI) by Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy.
• Utilization of Multi-Nuclear Magnetic Resonance spectroscopy of the D₂O extracts of the cycled anodes.
• IR spectroscopy is utilized to assist with the characterization of the electrolyte solution structure.

The latter portion of the presentation with cover a method for improving the energy density of lithium ion batteries by increasing the working potentials of positive electrode by employing lithium nickel manganese spinel LiNi_0.5Mn_1.5O₄ as the active material.

• The failure mechanism of graphite /LiNi_0.5Mn_1.5O₄ cells cycled at 25 °C and 55 °C (1.2 M LiPF₆ in 3:7 EC/EMC) analyzed by electrochemical methods and ex-situ surface analysis of the electrodes will be discussed
• Utilization of the mechanistic information about capacity fade in graphite/LiNi_0.5Mn_1.5O₄ cells  to develop novel additives to improve the performance of LiNi_0.5Mn_1.5O₄ cycled to high voltage (4.9 V vs Li) will be described.
• The details of our experimental results and our mechanistic interpretation will be presented.

This presentation looks at the development of alternate electrolytes for lithium (ion) batteries based on ionic liquid electrolytes. Ionic Liquids have been investigated in detail for the last 10 years and have physical and electrochemical properties that make them an excellent choice for use with high voltage cathode materials and enabling the next generation of lithium metal based batteries.

This presentation will cover:

• Who is CSIRO?
• What are ionic liquids?
• What makes ionic liquids and electrolytes thereof suitable for use in batteries?
• Historical development of ionic liquids for battery applications;
• What is state-of-the-art in terms of ionic liquid electrolytes today?

CSIRO has been a world leader in the research and development of ionic liquids and electrolytes thereof and we have examined a number of critical issues regarding their implementation in devices which I will cover in this talk:

• Electrochemical stability with intercalation electrode materials

• Graphite;
• LiFePO₄, LiCoO₂ and high voltage cathode materials;
• Al current collector corrosion; and
• Some device examples.

• Enabling the Lithium metal electrode

• Crucial for devices such as Li-S and Li-Air;
• Use of IL electrolytes to plate and strip Li in two-dimensions;
• Impedance of the Solid Electrolyte Interphase on Li; and
• Some device examples in Li-S.

• Cost and affordability of ionic liquid electrolytes

• Strategies to get these materials to market; and
• Blends of ionic liquids and aprotic solvents to reduce cost

The presentation will conclude with a discussion on how we might be able to make automotive battery packs that don’t require active cooling without compromising safety and performance.

Lithium ion batteries are now ubiquitous among consumer products and are poised to make significant contributions to other areas. There are safety shortcomings to this technology, with the potential for cell breakdown from overheating and/or thermal runaway. This is prevented by electronic devices but adds weight and additional cost to the battery. Another option for overcharge control is to use a redox shuttle. Research groups at Argonne National Laboratory have recently published some systems such as ANL-RS6 (4.8V) and ANL-RS5 (4.5V). The Materials Engineering Research Facility group at Argonne National Laboratory has successfully scaled up several shuttles for industrial evaluation. One of these (ANL-RS5) presented an initial process unsuitable for a large scale synthesis. We therefore developed a new synthetic route that emphasized scalability, and allowed a range of analogs to be tested. Electrochemical analysis of the analogs is currently underway.

• Introduction
• Background: Lithium Ion Battery
• Redox Shuttles
  • Synthesis and Performance of ANL-RS6
  • Synthesis of ANL-RS5
  • New RS5 Analogs
   
• Summary and Conclusion

Today’s lithium ion battery electrolytes are not reductively stable on graphite anodes at typical operating potentials.  Therefore, electrolyte additives are used that reductively decompose during the first cycle anode lithiation, forming a passivation layer that allows lithium transport, yet is electrically insulating to prevent further reduction of bulk electrolyte.  The properties and quality of the solid electrolyte interphase (SEI) layer are critical to achieving high cycle life, high rate performance, and wide operating temperature ranges for the battery.   To function effectively, such additives must both deposit uniformly on the electrode surface and form an electrochemically inert coating. These dual constraints severely limit the set of viable additives.

Wildcat Discovery Technologies has developed a new, modular additive concept in which additives are bound to a molecular core that enables uniform deposition on the electrode surface. Attachment of conventional additives to the core molecules provides improved SEI stability, resulting in increased coulombic efficiency, cycle life, and thermal stability. Furthermore, by decoupling the requirements for uniform coating and chemical stability, new classes of additives can be used.  In this talk, I will discuss the development of these modular additives as well as their performance in both commercial and future cell chemistries.

• Challenges in development of electrolyte additives with multiple constraints
  • Need for thin uniform film deposition
  • Need for electrochemical stability
  • Need for ionic conductivity
   
• Modular additive concept
  • Balance deposition properties vs. electrochemical performance
   
• Examples
  • Commercially available cell chemistries
  • Future cell chemistries
   

Wildcat Discovery Technologies uses a proprietary high throughput synthesis and screening platform for battery materials. Wildcat’s system produces materials in bulk form, enabling evaluation of its properties in a standard cell configuration. This allows simultaneous optimization of all aspects of the cell, including the active materials, binders, separator, electrolyte and additives.

Over the past 3 years, we have screened over 250,000 cells, developing new cathodes, anodes, and electrolytes for a variety of battery types (primary, secondary, aqueous, non-aqueous). In this talk, I will discuss what we’ve learned from this work, including:

• Overview of common failure modes in current and next-generation cells
• New analytical methods developed at Wildcat to predict performance at extended cycling and in large format cells:
  • High throughput, high precision coulombetry
  • High throughput, in-situ gas evolution
   
• Sensitivity of performance metrics to changes in cell components.
• Which performance metrics are most predictive of long term cycle life and other failure modes across all and specific electrode materials.

I will end with a discussion of best practices for electrode and cell evaluation.